I was in Portugal this week for a conference in memory of the economist Jose da Silva Lopes and I did some homework about the ter-rible times Portugal has recently suffered. What especially caught my eye was labor mobility (see the chart).

We used to think that high labor mobility was a good thing for cur-rency unions, because it would allow the union’s overall economy to ad-just to asymmetric shocks — booms in some places, busts in others — by moving workers around rather than having to cut wages in the lagging regions.

But what about the tax base? If bad times cause one country’s work-ers to leave in large numbers, who will service its debt and care for its retirees? Indeed, it’s easy conceptu-ally to see how a country could enter a demographic death spiral. Start with a high level of debt. If the work force shrinks because of emigra-tion, servicing that debt will require higher taxes on those who remain, which could lead to more emigration, and so on.

How realistic is this possibility? It obviously depends on having a suffi-ciently large burden of debt and oth-er mandatory expenditures. But it also depends on the elasticity of the working-age population to the tax burden, which in turn is contingent on the underlying economics — is there a strongly downward-sloping demand for labor, or is it highly elas-tic? — and on factors like the willing-ness of workers to move, which has

to do with culture and language.Portugal, with its long tradition

of out-migration, may be more vul-nerable than most other European countries, but I have no idea whether it’s really in that zone.

One thing you might wonder is whether a currency union makes any difference here. Can’t adverse shocks produce emigration and a death spiral regardless of the cur-rency regime? Yes, but: With a flex-ible exchange rate, adverse shocks will cause depreciation and a fall in real wages; under a currency union, they will produce unemployment for an extended period of time, or until

the grinding process of internal de-valuation restores competitiveness. And everything I’ve seen indicates that migration is much more sensi-tive to unemployment than to wage differentials.

Now, it’s true that emigration in an economy that has mass unemploy-ment doesn’t immediately reduce the tax base, since the marginal worker wouldn’t have been em-ployed anyway. But it does set things up for longer-run deterioration.

Despite all this, Lisbon remains very lovely — and seems, justifi-ably, to be attracting a lot of tourists, which must surely help the economy.

PAUL KRUGMAN

Is Emigration Making Portugal’s Situation Worse?

Due to a combination of ultralow fertility rates and mass emigra-tion, the populations of some European countries are shrinking, putting their economies at risk of becoming unsustainable.

Although the demographic situa-tion in the eurozone is alarming, mi-gration from debt-stricken nations in the south to more wealthy ones

in the north is making the situation worse for the peripheral economies, where older populations rely on an ever-shrinking working-age popula-tion to meet their needs.

— V., IRELAND

The recession that Portugal and other eurozone countries experi-enced between 2010 and 2014 was mainly caused by terrible deci-sions, which were then followed by a sequence of terrible events.

Among them:— After Lehman Brothers col-

lapsed, eurozone officials deter-

mined not only that no large bank should be allowed to fail, but that each country should be responsible for its own institutions. This policy, of course, illustrated a huge weak-ness with the common currency.

— The banks policy then caused severe capital flight from countries like Portugal that were exposed to large amounts of debt.

— Then came the troika-led inter-vention, followed by the implemen-tation of austerity policies, which then sparked a deep recession, high unemployment and emigration. Es-sentially, all this forced Portugal to undergo an internal devaluation, since currency devaluation was off the table.

— Meanwhile, the European economies with budget surpluses

decided to reduce their spending rather than increase investment, which then depressed aggregate de-mand across the eurozone.

— J. SOUSA, PORTUGAL

The problems are not merely debt and taxes. The people who are emigrating are often young, highly skilled and productive. Losing that portion of the work force greatly affects a country’s economic poten-tial, along with its social and moral values.

— BERTRAND, FRANCE

Your population chart is a poor illustration of your point, Mr. Krugman. It looks like immigrants moved to Portugal during the boom years between 1998 and 2002,

stayed until 2008 and left after 2010. The long-term effect on the popula-tion appears to be zero.

— S. TAYLOR, NEW YORK

Puerto Rico has experienced significant out-migration re-cently, which is causing the com-monwealth’s financial problems to become even worse than those of Portugal.

And yet, Mr. Krugman, you don’t seem to have a problem with Puerto Rico’s out-migration.

— A., FRANCE

This is a haunting article. I knew what was happening in Portugal, but I’m still saddened to see the situation depicted in this chart.

— NANCY, NEW YORK

We need a moratorium on high fertility. Unfortunately, liberals like you continue to deny the impact that population growth has on the envi-ronment and poverty.

— BLAISE ADAMS, CALIFORNIA

The stronger economies in the eurozone are in a good position to siphon off workers from the weak-er economies. This has had some negative effects, but perhaps it can have some positive ones as well.

For example, if enough people from the peripheral countries move to places like Germany and France, then perhaps there will be more support for having a political union in Europe, and not just a currency union.

— DAVE, WISCONSIN

READER COMMENTS FROM NYTIMES.COM

The Cost of Leaving

DANIEL RODRIGUES/THE NEW YORK TIMES

A plaza in Lisbon, Portugal. The country’s unemployment stands at about 13 percent.

DEBATING POLITICS, ECONOMICS AND OTHER TIMELY TOPICS WITH PAUL KRUGMAN OF THE NEW YORK TIMES FRIDAY, DECEMBER 18, 2015

ONLINE: COMMENTS Comments have been edited for clarity and length. For Paul Krugman’s latest thoughts and to join the debate online, visit his blog at krugman.blogs.nytimes.com.

I suppose that there are still some people waiting for Donald Trump’s bubble to burst — any day now! But it keeps not happening. And it’s be-coming increasingly plausible that he will go all the way to the Republi-can presidential nomination. Why?

One answer — probably the most important — is what Greg Sargent at The Washington Post has been em-phasizing lately: The majority of Re-publican voters actually support Mr. Trump’s policy positions. After all, he’s just saying outright what main-stream candidates have implied for years through innuendo — how are voters supposed to know that this isn’t what you do?

I would, however, add a casual ob-servation: At this point, Mr. Trump has been the front-runner for long enough that it’s very hard to imag-ine his supporters suddenly losing faith. That would be too embarrass-ing.

Bear in mind that embarrass-ment, and the desire to avoid it, are enormously important sources of motivation. Just consider what has happened to the supposedly smart guys who predicted six or seven

years ago that interest rates would soar and that we would see runaway inflation. Almost none of them have conceded that they were wrong or that they should have done more homework. Instead, many of them — especially the academics — have become ever more obsessed with claiming that they were somehow

right, or they’ve been trying to tear down the reputations of those of us who were right. Nobody likes look-ing like a chump, and most people will go to great lengths to convince themselves that they aren’t.

Now think about someone who has supported Mr. Trump since the sum-mer. For the Trump bubble to burst,

many people like that would have to slap their foreheads and say: “Wow, he’s not a serious person! What was I thinking?”

Very few people ever do that sort of thing. Someone who has spent months supporting Mr. Trump de-spite establishment denunciations — which is something like a third of Re-publicans — will go to great lengths to avoid conceding that he has been foolish. At this point, such people will insist that any negative reports about Mr. Trump are the product of hostile mainstream media. In fact, Mr. Trump’s very durability so far is likely to make him highly resilient in the coming months.

All this suggests that even if Mr. Trump’s candidacy does finally de-cline, his support is likely to flow not to an establishment candidate, but to another outsider figure. Everyone who knows Senator Ted Cruz well hates him. In this environment, that probably enhances his appeal.

The general election will, of course, be quite different. But it’s getting really hard to see how the Republican establishment reasserts control.

PAUL KRUGMAN

G.O.P. Has Gone Too Far to Turn Back Now

In the wake of a shooting in Cal-ifornia earlier this month, in which a married couple who were report-edly inspired by the Islamic State killed 14 people, Donald Trump, the Republican presidential candi-date, released a statement calling for “a total and complete shutdown of Muslims entering the United States until our country’s repre-sentatives can figure out what is going on.”

Mr. Trump’s campaign initially suggested that the ban would ap-ply to American citizens who are Muslim, but later clarified that the proposal would only apply to for-eign nationals.

The statement received near-universal condemnation from across the political spectrum — even from Mr. Trump’s rivals for the G.O.P. nomination, who have sometimes hesitated to challenge his positions for fear of offending Mr. Trump and his supporters.

However, in the days following Mr. Trump’s comments, his poll numbers among Republican vot-ers continued to rise, once again defying the predictions of ana-lysts.

While national polls show that strong majorities of Americans oppose Mr. Trump’s proposal, it remains popular among the Re-publican electorate. For instance, a recent poll conducted by NBC and The Wall Street Journal found that 42 percent of Republi-cans would support banning for-eign Muslims from entering the country, compared to just 36 per-cent who would oppose such a policy.

Mr. Trump’s statement about Muslims is only the latest in a string of controversies that have

defined his campaign. Early in his candidacy, Mr. Trump cautioned that many undocumented Mexi-can immigrants were “bringing crime” and potentially spreading “tremendous infectious disease.” Mr. Trump’s focus has since shift-ed to the perceived threat of Is-lamic terrorism. In recent weeks he has floated the ideas of regis-tering Muslims in a government database, and shutting down cer-tain mosques.

“While closing the country to foreign Muslims altogether is a radical idea relative to [America’s] founding ideals and current pol-icy, it is but an incremental step relative to the outer bounds of le-gitimate debate in the G.O.P. pri-mary,” wrote Brian Beutler re-cently in The New Republic. “The most surprising part of the latest Trump story is that it proves a Re-publican candidate can take Is-lamophobia too far for his party’s tastes.”

BACKSTORY

Proposal on Muslims Draws Condemnation

The key to understanding the Republican Party’s shift to the right is realizing that the moder-ates have all left the party, and that only far-right conservatives remain.

According to Gallup, only 28 per-cent of voters now identify as Repub-lican, compared with 38 percent who did in November 2004. Presumably, a large number of those who left were moderates who now consider themselves to be independents.

— JOHN M., MAINE

On Election Day, many of Mr. Trump’s supporters will realize

that the top job requires someone serious. Then, many will either vote for a Democrat in the privacy of the voting booth (because even a serious Democrat is less risky than Mr. Trump) or not vote at all (because they feel that neither de-serves their endorsement). Both of these options offer conservatives plausible deniability that they ever actually changed their minds about Mr. Trump.

— JIM, AUSTRALIA

We seem to live in an environ-ment in which embarrassment isn’t possible anymore within

certain media, political and finan-cial arenas. Otherwise, a former governor of California would no longer be making movies, people on their fourth marriages could not reverently intone “the sanctity of marriage” and industry titans could not bemoan evil tax men.

Embarrassment is only a factor when individuals are capable of feel-ing shame. If people are financially insulated and surrounded by enough sycophants, demagogues can con-tinue to spin and entertain as long as media outlets grant them the access to do so.

— R. LAW, TEXAS

I would caution readers to be mindful of Republicans’ feelings.

After all, conservatives do not like to be reminded that they were wrong about the economy, the effects of tax cuts for the rich, weapons of mass destruction in Iraq, climate change, the effectiveness of the governments in Iraq and Afghanistan, selling military-grade weapons to home-grown terrorists, Sarah Palin, race relations, marriage equality and right-wing militias on America’s southern border. You get the picture.

Never mind being embarrassed. I’d be ashamed.

— JOE, NEW YORK

READER COMMENTS FROM NYTIMES.COM

Conservatism, Without the Moderates

6,760,000

6,800,000

6,840,000

6,880,000

6,920,000

6,960,000

7,000,000

7,040,000

7,080,000

THE NEW YORK TIMESSource: Organization for Economic Cooperation and Development

Working-Age Population, Portugal

Note: The data represents people aged 15-64 in Portugal.

2000 2002 2004 2006 2008 2010 2012 2014

Paul Krugman joined The New York Times in 1999 as a columnist on the Op-Ed page and continues as a professor of economics and international affairs at Princeton University. He was awarded the Nobel in economic science in 2008. Mr. Krugman is the author or editor of 21 books and more than 200 papers in professional journals and edited volumes. His latest book is “End This Depression Now!”

RAY WHITEHOUSE FOR THE NEW YORK TIMES

Donald Trump, a Republican candidate for the presidential nomination, speaks at a rally earlier this month in Raleigh, N.C.