A former aide to Arizona Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE on Thursday blasted Mike Pence Michael (Mike) Richard PenceMcConnell locks down key GOP votes in Supreme Court fight Momentum growing among Republicans for Supreme Court vote before Election Day Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE, 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's running mate, for refusing to endorse McCain in his reelection bid.

"I remember traveling with John McCain to Indiana to campaign for, several times, for a desperate Mike Pence. Shame on him. #Karma," John Weaver tweeted Thursday.

I remember traveling with John McCain to Indiana to campaign for, several times, for a desperate Mike Pence. Shame on him. #Karma — John Weaver (@JWGOP) August 4, 2016

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Weaver, who worked on John Kasich's presidential campaign, went on to call the Indiana governor and former congressman "about as desperate a politician as one could find."

"McCain came in for him and made a difference. I was there. #shameful."

In 2000, Pence was about as desperate a politician as one could find. McCain came in for him and made a difference. I was there. #shameful — John Weaver (@JWGOP) August 4, 2016

Pence followed in Trump's footsteps Thursday by declining to endorse McCain, who is in a competitive primary race in Arizona.

"But the stakes in this election are so high. To restore our country and home and abroad, we need new leadership, and I'm looking forward to standing should to shoulder with Donald Trump to drive that new leadership forward," Pence told reporters at a campaign stop.

Trump said earlier this week McCain has not "done a good job for the vets."

Pence broke with Trump on Wednesday when he announced he "strongly" endorsed Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE's (R-Wis.) reelection, after the GOP nominee said he is "not quite there yet" on backing the House leader.

McCain is facing a difficult reelection race this year, with polls indicating that the Democratic nominee, Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE, has a shot at beating Trump in the state in November. The Arizona senator has been critical of Trump in the past.