WASHINGTON — Texas Sen. Ted Cruz enters tonight’s Republican presidential debate with a burst of momentum, a robust campaign infrastructure, and a target on his back.

It’s a shift for Cruz, whose campaign got off to a low-key start. Now, he’s challenging Donald Trump for the lead in the kickoff Iowa caucus and casting himself as a more electable alternative who still shares the bombastic billionaire’s anti-Washington appeal.

Trump and Cruz have been friendly on the campaign trail for months. But signs of a split have emerged in recent days, with Cruz appearing to question Trump’s judgment at a private fundraiser, according to audio obtained by The New York Times.