Jay Cost, a prominent political historian and influential conservative voice for The Weekly Standard, has quit the Republican Party.

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Cost, who wrote a scathing rebuke of Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE last month — “It's Time to Dump Trump” — imploring party members to dump their presidential nominee at the Republican National Convention in Cleveland, made his departure announcement Wednesday in a series of 13 tweets.

This is why my opposition to Trump has forced me out of the GOP. 1/ — Jay Cost (@JayCostTWS) July 27, 2016

Watching their moral backflips to defend his evident Putinism, or his astonishing ignorance, is simply appalling. 9/ — Jay Cost (@JayCostTWS) July 27, 2016

It's like what @seanspicer said about David Duke: at some point you get to a line that decent people can't cross. 11/ — Jay Cost (@JayCostTWS) July 27, 2016

It's indecent to defend Trump. I can defend flip-flopping—or attack it!—but I won't associate w/ a party led by so many indecent ppl. 13/13 — Jay Cost (@JayCostTWS) July 27, 2016

In lieu of voting for Trump, Cost says he plans to vote for Libertarian Party presidential nominee Gary Johnson Gary Earl JohnsonWhat the numbers say about Trump's chances at reelection Presidential race tightens in Minnesota as Trump plows resources into state The Hill's Campaign Report: Biden condemns violence, blames Trump for fomenting it l Bitter Mass. primaries reach the end l Super PAC spending set to explode MORE, a two-term Republican governor of New Mexico who served from 1995 to 2003.

Bill Kristol, the founder and editor of The Weekly Standard, has also been an outspoken critic of Trump, even going so far as to publicly search for a third-party alternative to the GOP nominee.