A co-founder of the Federalist Society, which famously compiled a list from which President Trump selected his two Supreme Court nominees, described the president's Thursday tweet about "delay[ing] the election until people can properly, securely and safely vote" as grounds for "immediate impeachment."

Northwestern University Law Professor Steven Calabresi wrote in a New York Times opinion piece published late Thursday that Trump "should be removed unless he relents" the sentiment expressed in the tweet.

Calabresi said he voted for Trump in 2016, and has voted Republican in every presidential election since 1980. He added that he staunchly defended Trump against what he called an "unconstitutional investigation by Robert Mueller" into alleged collusion with Russia and penned another op-ed opposing the president's impeachment earlier this year.

"But I am frankly appalled by the president’s recent tweet seeking to postpone the November election," he wrote. "Until recently, I had taken as political hyperbole the Democrats’ assertion that President Trump is a fascist.

STIREWALT ON TRUMP SUGGESTING ELECTION DELAY: 'FLAGRANT EXPRESSION OF WEAKNESS'

"But this latest tweet is fascistic and is itself grounds for the president’s immediate impeachment again ... and his removal from office by the Senate."

In the tweet, Trump slammed the prospect of mass mail-in voting as a prelude to the "most inaccurate and fraudulent election in history" and a "great embarrassment to the USA."

Calabresi emphasized that the U.S. "has never canceled or delayed a presidential election. Not in 1864, when President Abraham Lincoln was expected to lose and the South looked as if it might defeat the North. Not in 1932 in the depths of the Great Depression. Not in 1944 during World War II."

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The professor went on to say that the date of each election is fixed by an 1845 federal law and noted it is up to each state to determine whether they will implement universal mail-in voting, since "Article II of the Constitution explicitly gives the states total power over the selection of presidential electors."

Meanwhile, Calabresi called on "every Republican in Congress" to inform Trump that postponing the election would be "illegal, unconstitutional, and without precedent in American history.

"Anyone who says otherwise should never be elected to Congress again."