Story highlights Jeb Bush is carrying his crusade against Donald Trump to the doorstep of the Republican convention

Bush also actively floated supporting the Libertarian ticket in the fall

Washington (CNN) Jeb Bush is carrying his crusade against Donald Trump to the doorstep of the Republican convention, saying that he is not the future of the Republican Party even as it prepares to nominate him.

Bush, once seen as the front-runner for the Republican presidential nomination, remains one of the most prominent anti-Trump holdouts in the GOP. In an op-ed for The Washington Post published Friday, Bush acknowledged that Trump had capitalized on legitimate frustrations with American politics.

"They have given rise to the success of a candidate who continues to grotesquely manipulate the deeply felt anger of many Americans," Bush wrote, saying the nominee harkened back to an 1850s political party. "Trump's abrasive, Know Nothing-like nativist rhetoric has blocked out sober discourse about how to tackle America's big challenges."

Bush's op-ed continues his vehement opposition to Trump. During the primaries, he and Trump regularly traded shots on the campaign trail, with the real estate mogul memorably labeling him "low-energy." After Bush dropped out following the South Carolina primary, he vowed that he would not vote for Trump and does not plan to attend the Republican National Convention

Later Friday, he offered a backhanded compliment of Trump's decision to choose Indiana Gov. Mike Pence as his running mate , tweeting, "Mike Pence is a good man. He will add value to the ticket."

Mike Pence is a good man. He will add value to the ticket. — Jeb Bush (@JebBush) July 16, 2016

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