WASHINGTON — House Speaker Nancy Pelosi on Wednesday rescinded her invitation to President Donald Trump to deliver the State of the Union in the House next week — denying him a national platform for the annual speech in an extraordinary standoff between the two most powerful figures in the nation.

The cancellation — part of an escalating and at times personal feud between the newly elected Democratic speaker and the Republican president — illustrates the extent of the dysfunction that has gripped Washington and America’s body politic amid the longest federal government shutdown in U.S. history.

The imbroglio also underscores the extent of the enmity that has developed between Trump and Pelosi, neither of whom appears ready to retreat in their standoff over the president’s demand for money to fund part of his promised wall along the U.S.-Mexico border.

Pelosi and other Democratic leaders appear increasingly confident of their position in the fight as the impact of the government closures worsens while voters in numerous recent polls heap blame primarily on Trump and Republicans for the impasse.

The sparring has now led to the effective cancellation of a decades-old tradition in which presidents aimed to unify the nation, even in times of divided government. An annual show of unity has devolved into disunity.

“We’re supposed to be doing it, and now Nancy Pelosi — or ‘Nancy,’ as I call her — she doesn’t want to hear the truth. And she doesn’t want, more importantly, the American people to hear the truth,” Trump said at a meeting with conservative leaders at the White House.

Earlier Wednesday, Trump tried to call Pelosi’s bluff, saying he planned to honor the speaker’s invitation she extended earlier this month when the partial government shutdown was still in its relative infancy. Not delivering it in the House chamber, Trump wrote to her, would be “very sad.”

But later Wednesday, Pelosi, D-Calif., officially called off the address in the House chamber, asking instead for a new, “mutually agreeable” date once the government has reopened. Trump, faced with that reality, said he would be doing “something in the alternative.”

In a tweet late Wednesday night, Trump signaled a retreat, saying it was Pelosi’s “prerogative” to suggest a later date due to the shutdown. “I will do the Address when the Shutdown is over,” he said.

The squabbling extended a fight that erupted last week when Pelosi suggested to the president that they postpone the address, citing security concerns caused by the shutdown that were later dismissed by administration officials.

The historic partial government shutdown, now in its 33rd day, has left hundreds of thousands of federal employees without pay while the Trump administration began preparing for a funding lapse that could stretch into the spring.

Since President Woodrow Wilson in 1913, both Republican and Democratic presidents, with the House speaker and the vice president sitting behind them, have addressed the nation and Congress in a House chamber packed with members of the diplomatic corps, the Supreme Court, the Joint Chiefs of Staff, family members and guests.

Pelosi’s decision appears to be without precedent, as there seems to be no other instance of House speakers denying the use of the chamber for a president’s State of the Union, according to congressional historians.

“There’s none. There’s nothing close to it,” Tim Naftali, a presidential historian at New York University who is the co-author of the book “Impeachment: An American History.”

The challenge for Democrats, Naftali said, is to avoid giving the impression that they are reacting to Trump’s pettiness with their own.

“They should welcome hearing from him all the time,” Naftali said of Democrats, noting that one of the recent critiques of the White House is that it has cut back on media briefings. “He should be invited in a secure location wherever he wants to, and Democrats certainly shouldn’t give the impression that they’re boycotting” any speech Trump eventually gives.

In the battle over the border wall, both parties must be willing to compromise if they’re to break the impasse, Naftali added. “If you don’t allow both sides to emerge as winners, divided government results in paralysis.”

One similar parallel was in 1986, when President Reagan asked Speaker Tip O’Neill for permission to deliver a speech lobbying lawmakers on aid for contra rebels in Nicaragua in advance of a closely-watched vote. But O’Neill turned down the president’s request, which was not for a State of the Union. It was also under Reagan’s presidency that a State of the Union was last postponed Jan. 28, 1986 after the space shuttle Challenger exploded.

The Washington Post’s Mike DeBonis and John Wagner contributed to this report.