The Syrian refugee crisis is rapidly upending the debate over immigration in the 2016 presidential campaign.

For months, the discussion fixated on the unlikely quest by conservative voters and one leading candidate to deport millions of undocumented workers and build a wall—supposedly paid for by Mexico—on the Southern border. But the focus in the last two weeks has shifted from the question of how many people to kick out to the much more pressing imperative of how many refugees to take in.

Hillary Clinton on Sunday joined her rival Martin O’Malley in calling on the U.S. to accept as many as 65,000 refugees out of the estimated 4 million displaced by the chaos in Syria, where they have been caught between the civil war being fought by and against the Assad regime and the brutal crackdowns by the Islamic State as it seeks to hold and expand territory there and in Iraq. Clinton’s comments came in response to the announcement by her successor as secretary of state, John Kerry, that the U.S. would increase its annual cap on refugees to 100,000, although the number specifically from Syria would only go up by 10,000.

“I think the United States has to do more,” Clinton said on CBS’s Face the Nation.

And I would like to see us move from what is a good start with 10,000 to 65,000, and begin immediately to put into place the mechanisms for vetting the people that we would take in, looking to really emphasize some of those who are most vulnerable, a lot of the persecuted religious minorities, including Christians, and some who have been brutalized, like the Yazidi women.

The U.S. has accepted about 1,500 Syrians so far and is under pressure from human-rights groups and global allies to take many more. O’Malley, the former Maryland governor who is lagging well behind in the polls, issued his call for the U.S. to take 65,000 more than a week ago, which matches the request from the United Nations. Bernie Sanders, by contrast, who is generally more skeptical of immigration, has not specified how many refugees the U.S. should accept. “I think it's impossible to give a proper number until we understand the dimensions of the problem,” the Vermont senator said last week on Meet the Press.

The refugee question has divided the Republican field even further. While Donald Trump’s anti-immigrant rhetoric and his simultaneous rise in the polls this summer clearly pulled the GOP to the right on illegal immigration, the Syria crisis sets aside the debate over economics and enforcement, instead testing the candidates’ willingness to crack open the nation’s border on humanitarian grounds. None of the Republicans have thus far gone as far as O’Malley or Clinton, but Ohio Governor John Kasich is supporting the Obama administration’s plan to admit 10,000 more refugees from Syria in the next fiscal year. Lindsey Graham has said the U.S. should take an unspecified “fair share” of refugees, while Marco Rubio has said only that he is “open” to the possibility.

A universal concern cited by Republicans is the screening process for taking refugees and the possibility that Islamic extremists could slip into the country. “It is a bad idea if there is no screening,” Jeb Bush said on Fox News last week, adding that the U.S. should take “every Christian Iraqi and every Christian Syrian”who might be at grave risk. Ted Cruz said he opposed accepting “large numbers” of refugees that would be resettled rather than returned home, as did Bobby Jindal during the brief time that the issue was raised during last week’s GOP undercard debate. “The answer is not to put a Bandaid on this and allow even more people to come into America,” the Louisiana governor said. “We should not short-circuit; we have got a vetting process, we've got a normal refugee process. Simply allowing more into our country doesn't solve this problem.”

Rand Paul, meanwhile, repeatedly deflected the question when he appeared directly after Clinton Sunday on Face the Nation. “My first thought is that, you know, some of the arsonists should accept some of the refugees,” Paul said, referring to Saudi Arabia and other nearby countries that have balked at taking in people from Syria even as they have contributed to the chaos causing them to flee.

The urgency of the refugee question now also means that it could—hopefully—be moot by the time the next president takes office in 2017. But as hypotheticals go, pressing the candidates on how they’d handle a humanitarian immigration crisis in real time is probably more enlightening than asking them to debate mass deportation and border wall-construction. And at a moment when nativism appears to surging again among conservative voters, the Republican candidates in particular will have to weigh that restrictionist impulse against their simultaneous appeals to American exceptionalism, stronger leadership abroad, and a more muscular intervention in Syria and against ISIS. It's a complicated question, to be sure, but as the crisis escalates, it’s one that is quickly gaining in importance.