(CNN) - The co-founder of the conservative Federalist Society said Thursday in a blistering New York Times op-ed that President Donald Trump's tweet musing about a delay to November's presidential election is grounds for impeachment.
Steven Calabresi, a Northwestern University law professor who has offered broad defenses of the President in recent years, wrote, "I am frankly appalled by the president's recent tweet seeking to postpone the November election. Until recently, I had taken as political hyperbole the Democrats' assertion that President Trump is a fascist."
"But this latest tweet is fascistic and is itself grounds for the president's immediate impeachment again by the House of Representatives and his removal from office by the Senate," he said.
It's a significant break from the co-founder of one of the most influential groups in Republican politics. The Federalist Society has emerged as a leading conservative and libertarian voice in recent years, urging a limited role for judges in society's problems.
The group has also worked closely with Republican administrations to influence the selection of judges. Its leaders advised the George W. Bush administration on appointments and, for Trump, have become an even closer partner in screening candidates for the bench.
The scathing assessment comes hours after Trump explicitly floated delaying November's election in a tweet claiming without evidence that the contest will be flawed.
"With Universal Mail-In Voting (not Absentee Voting, which is good), 2020 will be the most INACCURATE & FRAUDULENT Election in history. It will be a great embarrassment to the USA," he wrote. "Delay the Election until people can properly, securely and safely vote???"
Trump has no authority to delay an election, and the Constitution gives Congress the power to set the date for voting. Lawmakers from both parties said almost immediately that there was no likelihood the election would be delayed.
"President Trump needs to be told by every Republican in Congress that he cannot postpone the federal election," Calabresi wrote. "Doing so would be illegal, unconstitutional and without precedent in American history. Anyone who says otherwise should never be elected to Congress again."
The op-ed, paired with an array of meaningful pushback on Trump from congressional Republicans on Thursday, offers a rare look at the limits on loyalty to the President within the GOP when it comes to defending his more extreme political urges.
Senate Judiciary Chairman Lindsey Graham, a South Carolina Republican and Trump ally, told CNN when asked about the President's call to delay the election: "I don't think that's a particularly good idea."
And Majority Whip Sen. John Thune of South Dakota, a member of Republican leadership, told CNN that there will be an election in November despite the President's tweet.
"I think that's probably a statement that gets some press attention, but I doubt it gets any serious traction," Thune said. "I think we've had elections every November since about 1788, and I expect that will be the case again this year."
Even with scores of Republicans openly challenging Trump's tweet, Calabresi's op-ed stand outs as a striking defection given his long history in the GOP. While he's offered some criticism of the President in the past, Calabresi has gained significant notoriety in recent years for his forceful repudiations of special counsel Robert Mueller's investigation as well as Trump's impeachment over his conduct with Ukraine.