Mitt Romney will take aim at Donald Trump in Thursday speech. Trump has already hit back.

Mitt Romney is taking his rebukes of Republican presidential frontrunner Donald Trump from Twitter and cable news to a bigger stage on Thursday morning, giving a speech on "the state of the

2016 presidential race" at the University of Utah. In his speech, Romney will likely hit Trump on his refusal to release his tax returns and his waffling over support from David Duke and the

Ku Klux Klan, sources tell Reuters. He won't endorse anyone, though he's expected to say nice things about Trump rivals Marco Rubio, Ted Cruz, and maybe John Kasich.

Donald Trump isn't taking this lying down. On Wednesday night, Trump took the unusual step of releasing an attack ad against Romney, posting it at his official Facebook page:

In what might be called an amazing display of chutzpah, Trump's ad accuses Romney of flip-flopping on several hot-button issues — health care, abortion — that Trump has flip-flopped on

himself, on camera. Maybe Fox News moderator Megyn Kelly will ask Trump about that at Thursday night's Republican debate.

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Peter has worked as a news and culture writer and editor at The Week since the site's launch in 2008. He covers politics, world affairs, religion and cultural currents. His journalism career

began as a copy editor at a financial newswire and has included editorial positions at The New York Times Magazine, Facts on File, and Oregon State University.