Mark Salter, the former chief of staff and speechwriter for the late Republican Sen. John McCain John Sidney McCainCindy McCain endorses Biden: He's only candidate 'who stands up for our values' Biden says Cindy McCain will endorse him Biden's six best bets in 2016 Trump states MORE (Ariz.), called on voters to vote Democratic on Election Day.

“Vote For the Democrat (in most cases),” Salter wrote on Twitter early Tuesday morning.

“That feels weird to write,” the ex-McCain staffer continued. “But the bigger the rebuke of Trump the better for the country. Resist.”

Vote For the Democrat (in most cases). That feels weird to write. But the bigger the rebuke of Trump the better for the country. Resist. — Mark Salter (@MarkSalter55) November 6, 2018

Salter's comments arrive as polls across the country open on Election Day with many waiting in anticipation to see whether a blue wave for Democrats will emerge in the first national elections since President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE took office.

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Salter, a longtime critic of the president, sparked headlines back in 2016 when he tweeted that he would back Democratic presidential nominee Hillary Clinton over Trump in the weeks leading up to the presidential election.

He’s also called out Trump for his "unstable personality” and recently dismissed Trump's attacks on the then-ailing McCain in May, saying on Twitter at the time that “the Senator doesn't give a rat's ass what this particular president says or thinks about him.”

McCain, another frequent critic of Trump's, died in August, about a year after being diagnosed with brain cancer.