Northwestern University Law Professor Steven Calabresi served in two Republican administrations, was an adviser to Attorney General Edwin Meese under Ronald Reagan and wrote speeches for Vice President Dan Quayle. He is co-founder and board chairman of the conservative Federalist Society.

So it raised a few eyebrows when Calabresi told a law school audience in San Francisco that when it comes to Donald Trump, “impeachment needs to be on the table.”

Even though both houses of Congress will be controlled by his fellow Republicans, Trump, a party outsider, will be “on a short leash. There could be a spectacular end,” Calabresi said in a recent panel at the annual meeting of the Association of American Law Schools.

Calabresi was a law clerk for Supreme Court Justice Antonin Scalia and another prominent conservative, Appeals Court Judge Robert Bork, and served in the Justice Department under Presidents Ronald Reagan and George H.W. Bush.

In the Reagan administration, he was an influential advocate of expanded presidential power and the use of “signing statements” declaring a president’s intention to disregard portions of a newly signed law. That became common under President George W. Bush.

Calabresi did find some things to praise about the incoming administration at the San Francisco panel discussion on Jan. 5.

He said former ExxonMobil CEO Rex Tillerson, Trump’s nominee for secretary of state, was right to advocate better relations with Russian leader Vladimir Putin, “to the extent that’s possible.”

He noted that former Marine Corps Gen. James Mattis, nominated for defense secretary, opposes waterboarding and other forms of torture. He said Iowa Gov. Terry Branstad, Trump’s pick to become U.S. ambassador to China, speaks Mandarin and is “beloved” in China. And he said choosing hard-line Alabama Sen. Jeff Sessions as attorney general was “a lot better than appointing your campaign manager (John Mitchell, by Richard Nixon) or your brother,” referring to Robert Kennedy, by John F. Kennedy.

But Calabresi said Republican leaders, who have lamented their party’s alienation from racial minorities, have been been dismayed by some of Trump’s comments on racial issues — for example, his claim that U.S. District Judge Gonzalo Curiel, of San Diego, presiding over a fraud suit by students against Trump University, was biased because of his Mexican heritage. Trump has since settled the suit for $25 million.

House Speaker Paul Ryan, R-Wis., has called Trump’s denigration of Curiel “the textbook definition of a racist comment.”

Calabresi said Trump had also displayed sexism — an apparent reference to his tape-recorded boasting of grabbing women by the genitals — and an out-of-control temperament. If Trump continues such behavior after taking office, Calabresi said, Republican leaders should consider impeaching him and replacing him with Vice President Mike Pence, who is much closer to his party’s establishment.

“He’s not a creature of the Republican Party,” Calabresi said of Trump. “He’s a creature of the swamp.”

His words may resonate more with Republicans than the dire forecasts from others on the San Francisco panel, and the law school community overall, since the election.

More than 1,300 law professors have signed a letter opposing Trump’s nomination of Sessions as attorney general. Last month, 42 constitutional law professors sent Trump a letter asking him to reverse his positions on such issues as abortion, freedom of the press and a proposed registry of Muslims in the United States.

Trump is “the least qualified person for the presidency ever,” UC Irvine law school Dean Erwin Chemerinsky, who signed both letters, said in the panel discussion. “I’m more scared for the country than I’ve ever been.”

Bob Egelko is a San Francisco Chronicle staff writer. Email: begelko@sfchronicle.com Twitter: @egelko