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(CNN) —  

Donald Trump accused former rival Jeb Bush of leading an effort among Republican delegates to block him from securing the nomination in Cleveland next month.

“By the way, Jeb is working on the movement, just so you understand. I love competition like that. I love it,” Trump said Saturday during a campaign rally in Las Vegas.

A former campaign spokeswoman for Bush, Kristy Campbell, quickly fired back Saturday, calling Trump’s “obsession” with Bush “unhealthy.”

“Donald Trump’s unending obsession with @JebBush is really unhealthy,” Campbell wrote.

Campbell referred CNN to her tweet when asked for comment on Trump’s assertion.

A group of Republican delegates, led by Colorado delegate Kendal Unruh, began organizing last week to change the convention rules so bound delegates could abstain from voting for Trump by citing a moral objection to him. The proposal could deny Trump the 1,237 delegates needed to secure the nomination, but it appears to face long odds.

Trump mercilessly mocked the one-time front-runner Bush as “low energy” throughout the primary campaign. But after Bush ended his campaign, many of his supporters went to work on #NeverTrump efforts.

Any effort to remove Trump still faces long odds – requiring the support of at least 1,237 delegates itself in order to block him.

The push to block Trump comes as Republicans have launched a preventative push to retain control of the House and Senate – amid signs that Trump is dragging down other Republicans in key swing states.

Jeb Bush’s brother, former president George W. Bush, has taken to the fundraising circuit on behalf of Senate candidates. They got some good news over the weekend, as supporters of Sen. Marco Rubio announced he is preparing to reverse course and run for re-election to his Senate seat.