In private conversations with several former aides, Mitt Romney, who in March will keynote the National Republican Congressional Committee’s annual fundraising dinner, has expressed rising frustration about Trump’s prolonged lead in polls and has argued that the real-estate mogul could inflict lasting damage on the party’s brand.

In Washington and elsewhere, meanwhile, Republicans are on the hunt for a political entity that can be used to stop Trump. In recent weeks, Alex Castellanos, a veteran TV ad man who was a top adviser to George W. Bush and Romney, has been meeting with top GOP operatives and donors to gauge interest in launching an anti-Trump vehicle that would pummel the Manhattan businessman on the television airwaves.

Those who’ve met with Castellanos say he’s offered detailed presentations on how such an offensive would play out. Castellanos has said that an anti-Trump ad campaign, which would be designed to cast him as a flawed strongman, would cost well into the millions. It was unclear, the sources said, whether Castellanos, who did not respond to a request for comment, would ultimately go through with the effort…

Cruz’s campaign pushes back on the idea that the Texas senator would imperil those running in House and Senate races. A Cruz nomination, they argue, would motivate conservatives to turn out to vote in a way that an establishment candidate couldn’t.