Hillary Clinton said she thinks Europe needs to “get a handle” on reforming immigration laws in order to fend off another Brexit.

Migration “is what lit the flame” of such nationalist movements, the former U.S. secretary of state told The Guardian for an upcoming series examining the rise of the populist right in the U.S. and Europe.

Conservatism and nationalist ideology have gotten a boost since Donald Trump won the U.S. presidency in 2016 and the U.K. voted earlier that year to exit the European Union. Although Clinton ran on a progressive immigration platform as Trump’s challenger, she essentially called for a retrenchment of those policies in The Guardian interview.

“I admire the very generous and compassionate approaches that were taken, particularly by leaders like Angela Merkel,” she said, praising the German chancellor for her open-door immigration policy. But Clinton added, “I think it is fair to say Europe has done its part, and must send a very clear message ― ‘We are not going to be able to continue to provide refuge and support’ ― because if we don’t deal with the migration issue it will continue to roil the body politic.”

Amid criticism of her comments, the former presidential candidate defended her statements in a series of tweets on Friday, saying she has “always been ... a staunch advocate of comprehensive immigration reform.”

“In a recent interview, I talked about how Europe must reject right-wing nationalism and authoritarianism, including by addressing migration with courage and compassion,” Clinton wrote on Twitter. “On both sides of the Atlantic, we need reform. Not open borders, but immigration laws enforced with fairness and respect for human rights.”

“The EU needs a more comprehensive policy that builds societies that are both secure and welcoming,” she added.

In The Guardian, Clinton condemned the fearmongering rhetoric often used by Trump when he discusses immigration in the U.S.

“The use of immigrants as a political device and as a symbol of government gone wrong, of attacks on one’s heritage, one’s identity, one’s national unity has been very much exploited by the current administration here,” she said.

“There are solutions to migration that do not require clamping down on the press, on your political opponents and trying to suborn the judiciary, or seeking financial and political help from Russia to support your political parties and movements,” Clinton added.