From flag-burning to libel, from conflicts of interest to torture, President-elect Donald Trump has made comments — in tweets, campaign orations and calm discussions — that have suggested he was either unaware of the applicable laws or didn’t care about them.

“Nearly every president has probably done something that a court has later held unconstitutional or contrary to law,” said Pamela Karlan, a Stanford law professor who recently served as supervisor of voting rights cases in the Obama administration’s Justice Department. “But I can’t think of one who had such an across-the-board combination of ignorance, indifference and defiance.”

“He’s consistently uninformed, and he’s consistently inconsistent,” said Jack Rakove, a Stanford professor of history and political science whose book about the origins of the Constitution won the Pulitzer Prize for history in 1997.

Rakove said the closest comparison might be Richard Nixon, who famously told an interviewer in 1977 — three years after resigning from office — that “when the president does it, that means it is not illegal.” But Nixon at least knew what the laws were when he ordered a cover-up of the Watergate break-in, he said.

Karlan offered another comparison, President Andrew Jackson. After the Supreme Court, led by Chief Justice John Marshall, ruled in 1832 that a U.S. treaty prohibited a state from seizing Cherokee land, Jackson allegedly said, “John Marshall has made his decision, now let him enforce it.” The government proceeded to ignore the ruling.

“Most presidents don’t talk that way,” Karlan observed. “Whatever presidents do, they express respect for laws in their public statements.”

Karlan was among more than 40 constitutional law professors to sign an open letter to Trump last week urging him to reconsider his views on several legal issues, including flag-burning and freedom of the press. One of Trump’s recent public statements was a tweet saying anyone who burned the U.S. flag should face “loss of citizenship or a year in jail.”

The Supreme Court had ruled in 1989 and 1990 that flag-burning was protected by freedom of speech — both 5-4 decisions in which Justice Antonin Scalia cast the deciding vote. In 1957, the court ruled, also 5-4, that Congress lacked the power to strip criminals of their citizenship as part of their sentence.

Scalia died in February, and Senate Republicans have refused to consider President Obama’s nomination of appeals court Judge Merrick Garland to succeed him. Trump has promised to choose someone like Scalia as his first court nominee.

“Despite his admiration for Justice Scalia, he appears to have a very different view of the First Amendment,” said Nate Persily, another Stanford law professor.

Trump’s war with the media — reminiscent of Nixon’s “enemies list” — included his pledge, at a campaign rally in February, to “open up our libel laws so when they write purposely negative and horrible and false articles, we can sue them and win lots of money.”

Libel laws, however, are enacted by the states, not the federal government. “Opening them up” to allow more suits by people in power would require a constitutional amendment to undo the limits established in a 1964 Supreme Court ruling, which requires government officials or public figures suing for libel to prove a statement about them was knowingly or recklessly false.

Despite occasional criticism from some in the legal community, including Scalia, the 1964 precedent has remained unscathed. Even a court with one or more Trump appointees would be unlikely to reconsider it, said Jonathan Turley, a Georgetown University law professor and longtime court commentator.

“This is the price of the life you choose when you become a celebrity,” Turley said.

Trump’s positions on torture by U.S. interrogators are more varied, as are his options.

During the campaign, he promised to bring back “waterboarding, and a hell of a lot worse,” even though international organizations and the Obama administration have condemned the near-drowning technique as torture. President George W. Bush had authorized waterboarding of suspected terrorists, but Obama prohibited it by executive order after taking office, and it was later banned by a bipartisan vote in Congress.

Later in the campaign, Trump acknowledged the congressional action and said he would get the law changed. But after the election, he appeared to back away from his claim that waterboarding worked. He said Gen. James Mattis, who has since become his candidate for defense secretary, told him interrogators got better results plying prisoners with “a pack of cigarettes and a couple of beers.”

But the president-elect hasn’t ruled out waterboarding, and he may be able to reauthorize it.

Because the law passed by Congress allows U.S. interrogators to use techniques permitted by the Army Field Manual, Trump could order the manual rewritten to permit waterboarding, although that might lead to a conflict with Mattis.

Trump could also emulate Bush, who obtained a permissive interpretation of the law from a Justice Department attorney — John Yoo, now a law professor at UC Berkeley — saying waterboarding isn’t torture and that even if it were, the president could order it as part of the war on terror.

The next president will have abundant sources of legal assistance, from Attorney General-designate Jeff Sessions to the attorneys in the White House, including White House Counsel Donald McGahn, who served as his campaign legal adviser, and every government department. But Karlan, the Stanford law professor and former Justice Department attorney, said the division where Yoo worked as a deputy — the Office of Legal Counsel, which advises the president on disputed questions of law — may be the most important from a public perspective.

The crucial question, she said, is, “Are those people going to enforce the law, tell him this is what the law says, and interpret it properly?”

Trump’s most pressing legal issue may be his far-flung business holdings, which could be affected in countless ways by government actions. While giving nonspecific assurances that he would remove himself from all business operations before taking office, he has shrugged off any potential for conflicts of interest.

“The law’s totally on my side, meaning the president can’t have a conflict of interest,” he told the New York Times last month.

It’s true that a federal conflict-of-interest law exempts the president and vice president. But the Constitution prohibits any U.S. official from accepting a payment from a foreign government. And in addition to that specific ban, the nation’s founding document is a potential source of some fundamental conflicts for a president who retains his business interests, Karlan said.

“He takes an oath to support and defend the Constitution,” she said. “If he does something for his business, he’s in conflict with the Constitution.

“If he invades a country because they put windmills outside his golf course, that would be a conflict of interest. If he decides not to enforce labor laws to protect workers at Trump casinos, that’s a violation of his oath of office. It’s the difference between having a king and having a president.”

But even if Trump did any of those things, he wouldn’t be prosecuted, Karlan said. The only recourse would be impeachment.

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