Sen. Mitt Romney, R-Utah, took to Twitter late Thursday to rip President Trump, saying the president had failed to make “even a plausible case of widespread fraud or conspiracy before a court of law” pertaining to the 2020 presidential election.

Romney said earlier this month that he did not have a problem with Trump challenging the election results and told “Fox News Sunday” he once considered challenging the 2012 election results when he lost to President Obama.

He said he thought it was “appropriate for the president to make sure that the vote count has been done properly.”

But Romney’s tone seemed to take a dramatic shift shortly after Rudy Giuliani made the case for the Trump campaign’s challenge of the 2020 election results.

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Romney took to Twitter and said, “Having failed to make even a plausible case of widespread fraud or conspiracy before any court of law, the President has now resorted to overt pressure on state and local officials to subvert the will of the people, and overturn the election. It is difficult to imagine a worse, more undemocratic action by a sitting American President.”

The post was a dramatic shot across the bow from a sitting senator from the same party, even though the two do not have a good relationship. 

Romney said he did not vote for Trump and voted to convict Trump for abusing presidential powers in February, after the House impeachecd the president.

Trump, back in June, mocked Romney for marching with protesters in Washington, D.C., to end “violence, and brutality, and to make sure people understand Black Lives Matter."

The president posted on Twitter at the time, “Tremendous sincerity, what a guy.”

Romney’s office told Fox News shortly after the tweet that there is a distinction between “pursuing legal challenges” where evidence exists, “and the harmful and damaging rhetoric that the election is rigged.”

His office also said “it goes without saying that applying political pressure to local officials not to certify legally cast ballots is outside the bounds of any regular legal challenge.”

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The Associated Press reported that a person familiar with the matter said Trump himself reached out to the Republican canvassers in Michigan’s Wayne County on Tuesday evening after they reversed their decision to certify the election results, and to express gratitude for their support.

The Trump 2020 Campaign did not immediately respond to a Fox News request for comment.