On Thursday night, just days before the Iowa caucuses, Ted Cruz, Marco Rubio, and Jeb Bush stood on the debate stage tussling over who had the stronger stance on immigration. The issue provided the signature moment of a debate that Donald Trump skipped—a mark of how profoundly Trump’s candidacy has shifted the discussion of immigration.

Fox News, in an unprecedented move, prepared footage of the candidates’ reversals on the issue, asking them to explain their inconsistencies. First up was Marco Rubio. In 2013, the Florida senator sponsored the “Gang of Eight” bill, a reform package that included a path to citizenship for some of the 11 million undocumented immigrants already in the country. Rubio has since reversed his stance and has said that he opposes amnesty. On Thursday night, Bush said Rubio had decided to “cut and run because it wasn’t popular.” Rubio quipped that Bush had also supported a path to citizenship, referring to a book Bush wrote on immigration. To which the former Florida governor shot back, “so did you.”

Next up were clips of Cruz on the Senate floor proposing to add an amendment to the Gang of Eight immigration-reform bill. Cruz argues that the amendment was meant to kill the bill. Rand Paul didn’t buy it, accusing Cruz of hypocrisy. “What is particularly insulting, though, is that he is kind of saying, ‘Oh, you’re for amnesty.’ Everybody is for amnesty but Ted Cruz. But it’s a falseness,” adding “that’s an authenticity problem, that everybody he knows is not as perfect as him.”

But for all the heat, there was very little light shed on what actions the candidates would actually take on immigration. And this is where Donald Trump comes in.

The Republican frontrunner has tapped into voters’ anger on the issue. Though absent from the stage on Thursday, Trump’s aggressive rhetoric has set him apart on immigration. Rewind a few months, to Trump’s announcement of his candidacy, when he remarked that Mexican immigrants were criminals and rapists. That fueled his rise and, as a result, redefined the debate on immigration.

On Thursday night, Rubio accused Cruz of wanting to “trump Trump on immigration,” even as he vied to do precisely that himself. The “Gang of Eight” bill had been Rubio’s signature legislative initiative in the Senate. But, as my colleague Peter Beinart noted earlier this month, the people Rubio needs to win are strongly opposed to undocumented immigration, illuminating the disconnect between his position then and now.

Candidates have loudly proclaimed their opposition to amnesty, but campaign-trail pledges have often given way to the practicalities of legislative compromise before. Rubio and Cruz were involved in such efforts in 2013, but they’ve now reversed their positions, as they try to appeal to voters’ resentments. All the candidates have denounced Obama’s executive actions that would shield undocumented immigrants from deportation. But how they would actually resolve the challenges of immigration remains an open question.