WASHINGTON — Donald Trump's best ally in winning over skeptical Republicans is turning out to be Hillary Clinton.

Having overcome a multimillion-dollar "Never Trump" campaign aimed at blocking him from the Republican nomination, he's now benefiting from a wave of GOP donors, party leaders, voters and conservative groups that are uniting under a new banner: "Never Hillary."

"Nothing unites Republicans better than a Clinton," says Scott Reed, a political strategist for the U.S. Chamber of Commerce who has advised previous GOP campaigns. While Reed says there remain "many unknowns" about Trump, he adds that "the knowns about Hillary are very powerful motivators to Republicans."

Thanks to Republicans' deep disdain for the likely Democratic nominee, Trump is piling up those kinds of lukewarm GOP endorsements.