The cash-rich group aiding Jeb Bush’s White House run has filmed a provocative video casting his rival Marco Rubio as ultimately unelectable because of his hard-line stand against abortion…

Seething with anger and alarmed over Mr. Rubio’s rise, aides to Mr. Bush, the former Florida governor, and his allies are privately threatening a wave of scathing attacks on his former protégé in the coming weeks, in a sign of just how anxious they have become about the state of Mr. Bush’s candidacy…

Whether or not the onslaught ever materializes, Mr. Rubio and his team are bracing for it and preparing to counter it by sifting through hours of video footage for instances in which Mr. Bush spoke about Mr. Rubio as an admiring ally, not a political foe.

They are also telegraphing a warning that has already reached many of Mr. Bush’s donors: Such an assault, they argue, would be beneath the dignity of the Bush name. And Mr. Bush should focus on resurrecting his own candidacy, they say, not on trying to tear down Mr. Rubio, who they contend represents the future of the Republican Party…

For many of Mr. Bush’s longest-serving advisers, Mr. Rubio’s run is a betrayal: Mr. Bush backed Mr. Rubio’s bid for House speaker in Florida and persuaded important donors to endorse him for the Senate. A few of Mr. Bush’s supporters have taken to calling Mr. Rubio “Judas.”