Donald Trump faced a deadline of midnight on Thursday to say if he would appear before a Washington grand jury convened by the special counsel Jack Smith to consider federal charges over his election subversion and incitement of the attack on Congress on 6 January 2021.

Late on Wednesday, citing two people familiar with the matter, the Guardian reported that prosecutors had assembled evidence to charge Trump with three crimes.

They were: obstruction of an official proceeding, conspiracy to defraud the United States, and an unusual statute that makes it unlawful to conspire to violate civil rights.

Obstruction of an official proceeding is punishable by up to 20 years in prison. Conspiracy to defraud the United States carries a maximum five-year sentence. The civil rights charge is punishable by up to 10 years in prison.

By Thursday afternoon, all indications were that Trump would not agree to testify.

Indictments regarding Trump’s attempted election subversion are expected soon – not only at the federal level but also in Fulton county, Georgia, where a grand jury to consider charges was recently formed. Elsewhere, this week saw charges brought against 16 people in a “false electors” scheme in Michigan, another battleground state.

On Thursday morning, meanwhile, Politico reported that Trump had extracted a promise from the Republican speaker of the US House of Representatives, Kevin McCarthy, to hold votes on expunging Trump’s two impeachments.

Trump was impeached first for withholding military aid in an attempt to extract political dirt from Ukraine, then for inciting the Capitol attack. In both cases, Senate Republicans ensured his acquittal at trial.

Trump reportedly got the promise of an expungement vote, which Politico said McCarthy “made reflexively to save his own skin”, after the speaker provoked outrage from Trump allies by declining to endorse the former president in the Republican presidential primary for the 2024 election, citing an obligation to remain neutral.

An expungement vote would be purely symbolic. It also would not be guaranteed to succeed. Republicans control the House by a very slim majority. Two sitting GOP congressmen, David Valadao of California and Dan Newhouse of Washington state, voted to impeach Trump over the Capitol riot. Republicans in swing districts, particularly in heavily Democratic north-eastern states, already face uphill fights to keep their seats.

Speaking to reporters on Thursday, McCarthy denied making a promise, saying “There’s no deal” with Trump, but added: “I’ve been very clear from long before – when I voted against impeachments – that [Democrats] put them in for purely political purposes. I support expungement but there’s no deal out there.”

In polling averages for the Republican primary, Trump leads by about 30 points. He has maintained that lead even while facing 34 criminal charges in New York, over hush-money payments to the porn star Stormy Daniels; 37 federal charges over his retention of classified documents; the prospect of state and federal indictments over his election subversion; a $5m fine after being held liable for sexual abuse and defamation against the writer E Jean Carroll; and ongoing investigations of his business affairs.

Denying all wrongdoing, Trump has pleaded not guilty to all criminal charges.

Nonetheless, polling regarding a notional general election shows him in a close race with Joe Biden. Earlier this week, Miles Taylor, who was a US homeland security official when in 2018 he wrote a famous anonymous New York Times column warning of Trump’s unfitness for office, told the Guardian Trump could yet return to the White House.

“There’s been a number of polls that show the ex-president beating Joe Biden by several points,” Taylor said. “It would be hubris to say, ‘Oh, no, we would beat him again a second time.’ Actually, I don’t think that. If the election was held today, I think Donald Trump would defeat Joe Biden, and that really concerns me.”

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Taylor also pointed to the supine nature of the Republican party, saying McCarthy, the House speaker, “thought Trump was a buffoon and a danger and I’m sure Kevin still thinks that privately” but is unwilling, or unable, to move in any way against him.

Taylor said: “Those people publicly, because they’re afraid, are still supporting the man. That collective anonymity is putting us in pretty seriously great danger.”

Trump revealed on Tuesday that Smith had told him he faced potential charges. According to the New York Times, since then Trump has consulted with Washington allies including McCarthy and the New Yorker Elise Stefanik, chair of the Republican House conference and a staunch supporter who many observers think is eyeing selection as Trump’s running mate next year. Miles Taylor seen in Washington DC, shortly after revealing his authorship of a famous New York Times column and book. ‘Trump can beat Biden’: White House whistleblower Miles Taylor returns with fresh warning Read more

Trump’s closest challenger for the Republican nomination, Ron DeSantis, this week mildly criticised Trump for his inaction on 6 January 2021, as the Capitol was attacked, but also said charges against the former president over his election subversion would not “be good for the country”.

Court dates are set to clash with the Republican primary calendar. Trump faces three civil trials in New York, one to begin in October and two in January.

In the criminal cases, Smith, the special counsel, has asked for trial over the classified documents charges to begin later this year. In the hush-money case, the trial is scheduled for March – in the thick of the Republican primary. Lawyers for Trump are attempting to delay both trials until after the general election next year, when Trump or another Republican president could order all cases dropped.

On Thursday, Benjamin Ginsberg, a Republican elections lawyer, told the Washington Post the US was “in as precarious a situation as we’ve ever been”.

“I don’t know what the chances are of things really going off the rails,” Ginsberg said, “but no question that there is a toxic mix unprecedented in the American experiment.”