President Trump drew immediate rebukes from across the political spectrum Thursday after proposing a delay to the November election and claiming without evidence that widespread mail balloting would be a “catastrophic disaster” leading to fraudulent results.

The suggestion represented Trump’s latest, and most dramatic, attempt to undermine public faith in the Nov. 3 election, a trend that has grown more frequent and emphatic as polls have shown his political fortunes declining. The president has attacked mail voting nearly 70 times since late March in interviews, remarks and tweets, including at least 17 times this month, according to a tally by The Washington Post.

Thursday’s tweet came on the heels of a devastating report showing that the economy shrank nearly 10 percent from April through June, the largest quarterly decline since the government began publishing such data 70 years ago.

The president does not have the authority to change the date of the general election, which is set by Congress. Trump encountered unprecedented pushback to his idea from senior Republicans on the Hill and conservative leaders outside government, as well as legal scholars, historians and Democrats.

Former president Barack Obama, speaking at the funeral of the late civil rights icon John Lewis in Atlanta, alluded to the intensifying war over voting rights, saying that “even as we sit here, there are those in power who are doing their darndest to discourage people from voting.” Obama, who has avoided public comments on much of Trump’s presidency, did not specifically cite his successor’s latest suggestion or mention him by name.

Senate Majority Leader Mitch McConnell (R-Ky.) was among many Republican senators who quickly and unequivocally rejected Trump’s idea. “Never in the history of the country, through wars, depressions and the Civil War, have we ever not had a federally scheduled election on time,” McConnell said in a television interview with WNKY of Bowling Green, Ky. “We’ll find a way to do that again this Nov. 3.”

Trump gave no indication that he would launch a serious push for the date change, or that he thinks he has the power to do so without congressional approval. But he appeared unfazed by the criticism.

He “pinned” the tweet in which he first floated the idea Thursday, fixing it to the top of his Twitter feed.

“With Universal Mail-In Voting (not Absentee Voting, which is good), 2020 will be the most INACCURATE & FRAUDULENT Election in history,” he wrote in the message. “It will be a great embarrassment to the USA. Delay the Election until people can properly, securely and safely vote???”

At a news conference late in the day, Trump said does not want to delay the election, but said the alternative is a “crooked election” that could be take months or even years to resolve — suggesting he is prepared to contest the results if he loses.

“I want to have the election,” he said. “But I also don’t want to wait for three months and find out that all the ballots are all missing and the election won’t mean anything. That’s what’s going to happen, and everyone knows it.”

Several Trump advisers said no internal discussions were underway within the White House about moving the date. The tweet caught aides by surprise, said one senior adviser who, like others, spoke on the condition of anonymity to describe internal conversation. “He is just trolling,” said another.

The U.S. Constitution gives the power to regulate the “time, place and manner” of general elections to Congress, while states control the dates of primary elections. Nowhere is the president granted such power.

In addition, the Constitution’s 20th Amendment spells out a hard end to a president’s and vice president’s four-year terms on Jan. 20, whether an election is held or not.

“The President has no power to change the date of the election,” said Richard L. Hasen, a law professor at the University of California at Irvine. “This is yet another statement by the President which undermines voter confidence and that seeks without evidence to undermine the legitimacy of voting by mail.”

No president has ever before tried to postpone a federal election, said historian Michael Beschloss. The idea was floated to President Abraham Lincoln in 1864, during the Civil War, and to President Franklin D. Roosevelt in 1942, during World War II.

Lincoln said at the time that postponing an election because of the “Southern rebellion” would mean “our system has been defeated,” while Roosevelt said doing so while fighting the fascists would mean “we have become fascists ourselves,” Beschloss said.

“That tweet claims powers that he does not have, period,” he said. “He is not a dictator.”

One of the most dramatic critiques of Trump’s tweet came from Steven G. Calabrese, a co-founder of the conservative Federalist Society, who wrote in an opinion piece published in The New York Times Thursday that the idea was “fascistic” and “grounds for the president’s immediate impeachment.”

Trump has enjoyed full-throated support from conservatives and nearly all congressional Republicans; the Federalist Society, for instance, has cheered on and even helped select his Supreme Court nominations. That backing appeared to wobble on Thursday, with many Republicans not only alarmed by the president’s apparent disregard for the limits of his power, but emboldened to say so in public.

“Election Day is and will be Nov 3, 2020,” said Republican Ari Fleischer, a former press secretary to George W. Bush. “Mr. President — please don’t even pretend to mess with this. It’s a harmful idea.”

Added Rep. Liz Cheney (R-Wyo.) on Twitter: “We are not moving the date of the election. The resistance to this idea among Republicans is overwhelming.” Sen. Marco Rubio (R-Fla.), Sen. Lindsey O. Graham (R-S.C.) and House Minority Leader Kevin McCarthy (R-Calif.) weighed in similarly.

House Speaker Nancy Pelosi (D-Calif.), meanwhile, simply tweeted the relevant passage from the Constitution granting Congress the power to set election dates. Joe Biden, the presumptive Democratic nominee, told supporters at a virtual fundraiser Thursday that Trump was probably trying to steal attention away from Lewis’s funeral.

Other Democrats suggested that Trump’s suggestion reflected a realization that he could lose to Biden, who has been leading in national and many battleground state polls.

“Donald Trump is terrified,” tweeted Sen. Kamala D. Harris (D-Calif.), who is among those being considered as a running mate for Biden. “He knows he’s going to lose to @JoeBiden. It will require every single one of us to make that happen. We will see you at the ballot box on November 3rd, @realDonaldTrump.”

Some Democrats used the occasion to promote how-to instructions on mail balloting.

“President Trump is talking about delaying the November election because he is afraid of people voting by mail,” Rep. Donna Shalala (D-Fla.) said in a tweet, in which she included a link to a Florida government website with instructions on how to do so. “You know what to do,” she added.

The president of the American Postal Workers Union, Mark Dimondstein, also rebuked the president for undermining confidence in the U.S. Postal Service. He noted that there is “essentially no fraud” in mail balloting.

“It’s a tremendous insult for the president be railing against vote by mail over and over and over and over, railing against the post office,” Dimondstein said. “It’s an insult to every postal worker and every customer who trusts the post office.”

Ronna McDaniel, chairwoman of the Republican National Committee, said on Fox Business that “obviously” the president understands that he doesn’t have the authority to move the election.

A Justice Department spokeswoman declined to comment on Trump’s tweet. Earlier this week at a House Judiciary Committee hearing, however, Attorney General William P. Barr told Rep. Cedric L. Richmond (D-La.) he had not studied the question of whether the president could move the election date.

“I’ve never been asked the question before. I’ve never looked into it,” Barr said.

Biden suggested in April that Trump might try to move the election date. At the time, Trump campaign spokesman Tim Murtaugh accused Biden of “incoherent, conspiracy-theory ramblings” and said the president “has been clear” that the election will happen on Nov. 3.

Another Trump campaign spokesman, Hogan Gidley, said in a statement Thursday that the president was merely “raising a question about the chaos Democrats have created with their insistence on all mail-in voting.”

In fact, most Democrats are pushing for mail balloting in addition to early in-person and Election Day voting — not universal mail balloting, as Trump has alleged — because even though many voters have expressed a new preference for voting by mail because of fear of infection, many other voters remain more comfortable casting their ballots in person.

Trump has argued that mail-in voting tends to hurt Republicans at the ballot box, but some Republicans worry that the president’s own rhetoric is what’s turning their own voters off of mail balloting.

A Washington Post-ABC News poll conducted this month shows that 51 percent of Democrats prefer voting by mail this fall, compared with 20 percent of Republicans. A recent study by Stanford University researchers found no partisan impact of expanding voting by mail.

At the congressional hearing, Barr repeated his concern that he felt there was a “high risk” that mail-in voting would lead to fraud, but said he did not believe the election would be rigged — seeming to break with Trump.

“I have no reason to think it will be,” Barr said.

Even if Congress voted to delay the general election, the electoral college is still required to elect a president under federal law. If lawmakers changed that, too, Trump and Vice President Pence would still be required to leave office by noon on Jan. 20. With no successor, the speaker of the House of Representatives, currently Pelosi, would be next in line.

Elise Viebeck, Scott Clement, Matt Zapotosky, Erica Werner, Jacob Bogage, Seung Min Kim, Annie Linskey and Devlin Barrett contributed to this report.