WASHINGTON - It was a month after the 2020 presidential election, and Bernard Kerik was starting to panic. The former New York City police chief and his friend Rudy Giuliani were shelling out thousands of dollars for hotel rooms and travel in their effort to find evidence of voting fraud and persuade state legislators to overturn Joe Biden's victory.

Yet President Donald Trump's campaign had turned down Kerik's request for a campaign credit card. The bills were piling up. "How do I know I'm gonna get my money back?" Kerik remembers thinking to himself at the time, according to a recent interview he did with The Washington Post.

The bills went unpaid until after Fox News personality Jeanine Pirro went to bat on their behalf, according to a Republican official, who like some others interviewed for this article spoke on the condition of anonymity to discuss private conversations. Soon after, the campaign cut Kerik a check - with Trump's approval, according to a former senior campaign official.

That move, in mid-December, smoothed the way for what would eventually be more than $225,000 in campaign payments to firms owned by Kerik and Giuliani - including more than $50,000 for rooms and suites at the posh Willard hotel in Washington that served as a "command center" for efforts to deny Biden the presidency in the days leading up to the attack on the Capitol on Jan. 6.

The fact that campaign funds were used to finance efforts to subvert Biden's victory could complicate the former president's ongoing attempt to use claims of executive privilege to shield documents and testimony from the Congressional committee investigating Jan. 6, according to some legal scholars.

The Congressional panel has made sweeping requests to the archivist of the United States for papers from the Trump White House, including for all documents stretching back to April 2020 that relate to efforts to challenge the results of the election or delay the counting of electoral college votes.

The requests specifically name dozens of people, including Kerik, Giuliani and others who were present in the Willard command center, such as former White House strategic adviser Stephen Bannon and legal scholar John Eastman. Eastman wrote two memos laying out legal arguments for Vice President Mike Pence to either reject Biden's electoral votes on Jan. 6 or delay certifying the results so that states could conduct further investigations.

Trump has asked a federal court to block the release of the documents, claiming that they are protected by executive privilege. And Bannon, facing a subpoena from the committee, has cited Trump's executive privilege claims as a reason for his refusal to comply.

The use of campaign funds "further undermines a wildly broad assertion of executive privilege" by Trump, said Richard Ben-Veniste, a former Watergate prosecutor. "Executive privilege is typically limited to the protection of communications involving a president's official duties - not to those relating to personal or political campaign matters," Ben-Veniste said.

The lawyer Alan Dershowitz disputed that assessment, claiming that "a lot of things that are done on behalf of an incumbent president are done by campaigns."

But former Justice Department official John Yoo agreed with Ben-Veniste. "If he acts as a president, he gets these things we talk about - executive privilege and immunity. But if he's acting as a candidate, he's deprived of all of those protections," said Yoo, one of the stalwart conservative legal scholars who advised Pence's staff that there was no basis for the vice president to intervene in the counting of electoral votes on Jan. 6.

Taylor Budowich, a spokesman for Trump, said that the former president "is making executive privilege determinations carefully, based on the merits and in accordance with law and customs of interbranch comity." He accused the Biden administration of "jeopardizing the office of the presidency by refusing to assert privilege over clearly privileged documents."

Robert Costello, a lawyer representing both Giuliani and Bannon, declined to comment.

One day after the election, Kerik arrived at Trump campaign headquarters in Arlington, Va., to help Giuliani, his friend and former boss. Kerik said he expected to find a bustling legal operation with staffers working overtime to ramp up investigations of election fraud.

Instead, he said, he found Giuliani with only a skeleton staff in a giant conference room.

In the early days of their post-election fight, they and others stayed at the Mandarin Oriental in downtown Washington while working out of the Trump campaign headquarters across the Potomac, according to Kerik.

But after a case of COVID at campaign headquarters, the Mandarin became their office, too.

"We had actually people from a number of federal agencies that came to see [Giuliani] - state legislators, staffers from members of Congress," said one person familiar with the operation at the Mandarin, who declined to name individuals. "That happened to be our office and headquarters, our command room - whatever you want to call it. That's where we were."

Giuliani and the team in Washington focused on making the case to the public and to legislators in key states, trying to persuade them that they were empowered by the Constitution to switch their state's electoral votes to Trump.

In those first weeks, Kerik put some of the bills for Giuliani's operation on his personal credit card, including part of the extended stay at the Mandarin.

Kerik said he also covered hotel rooms, travel, transportation and food for a trip the team took to Lansing, Mich., in early December. During that trip, Giuliani presented debunked claims of election fraud to the Michigan House Oversight Committee and encouraged lawmakers to "take back your power" and intervene in the 2020 election.

The balance due on Kerik's credit card was climbing, and he knew that Giuliani had not yet been reimbursed for his expenses or paid for his services.

Republican National Committee Chairwoman Ronna McDaniel agreed to speak to Kerik after Pirro - a friend to both Kerik and Giuliani - called and urged her to do so, according to the Republican official familiar with Pirro's intervention. Pirro had also been close to Trump for years; on the last day of his presidency, he granted a pardon to her ex-husband, Albert Pirro Jr., who had served 11 months in prison for tax evasion and other crimes.

Though McDaniel got on the phone with Kerik, she refused to give him money, advising him instead to call the Trump campaign, according to Kerik and the GOP official.

Kerik - also a recipient of a Trump pardon, granted in February 2020, for tax offenses and other crimes - said he was unaware of Pirro's call but not surprised she would try to help. Pirro did not respond to requests for comment. An RNC spokeswoman declined to comment. The RNC has repeatedly said that it did not pay Giuliani or Kerik because it did not hire them.

Kerik previously told The Post he was "furious" with the RNC because it raised tens of millions of dollars to support Trump's legal battle, "yet didn't spend a dime on [Giuliani's] legal team or their expenses."

Trump had directed aides not to pay legal fees for Giuliani, whose associate had sent a message on his behalf, seeking $20,000 a day for his work. But the president did agree to pay post-election travel expenses, according to the senior campaign official.

Kerik billed the Trump campaign on Dec. 6, seeking $20,130.13 for "Room/Board/Meals/Travel for Legal/Investigative Team" from Nov. 5 to Dec. 5, according to documents reviewed by The Post. He was reimbursed for the full amount on Dec. 18, campaign finance disclosures show.

Also on Dec. 18, the campaign made a payment of $63,423.63 to Giuliani's firm, Giuliani Partners. In campaign finance disclosures to the Federal Election Commission, the purpose was listed as "recount: travel reimbursement." The nature of the expenses was not further detailed in documents reviewed by The Post.

According to two former senior Trump campaign officials, lawyers for the campaign and the RNC viewed the Giuliani group warily, and there was minimal collaboration between the two groups and the Giuliani team after Trump made clear in mid-November that he wanted Giuliani to be in charge of efforts to challenge Biden's victory.

Some campaign staffers thought the Giuliani team was spending too much on hotel accommodations. "They could have rented an apartment if they were staying for an entire month," said one former senior campaign official.

In mid-December, the team moved from the Mandarin to the Willard, documents show. From the command center there, the team worked to make the case to Pence that he could interfere with the counting of electoral college votes on Jan. 6. To maximize pressure on Pence, they also sought to rally support from legislators in key states and from the Trump-supporting public.

According to documents reviewed by The Post, the team at the Willard included Kerik and lawyer Jenna Ellis, who had traveled around the country with Giuliani in the weeks after the election, presenting legislators in key states with alleged evidence of fraud.

On Jan. 3, they were joined by Eastman, the legal scholar. Eastman met with Trump and Pence the following day in the Oval Office, where he urged Pence to delay the counting of electoral votes so that state legislators could have more time to investigate supposed fraud.

Also at the Willard was lawyer Katherine Friess, whose firm - Seven Good Stones - was used to reserve the rooms at the Willard, according to Kerik and documents reviewed by The Post.

Friess did not respond to several requests for comment.

Around the time the team set up shop at the Willard, Trump, Giuliani and a phalanx of others seeking to overturn the election often cited a "forensic report" on Dominion Voting Systems machines as proof that the presidency had been stolen. The report was written by Russell Ramsland, a Texas tea party activist who had previously written affidavits that, though riddled with errors and baseless claims, were submitted as evidence in multiple lawsuits challenging Biden's victory.

Ramsland's report, released as part of a court case alleging fraud in Antrim County, Mich., was based on copies of Dominion hard drives. Friess was one of seven people who were part of the "forensic team" present for the copying of those hard drives on Dec. 6, court records show.

Phil Waldron, a retired Army colonel who specialized in psychological operations, was listed as an expert witness in the Antrim County lawsuit that gave rise to the "forensic report." The Post previously reported that Waldron was among those working out of the Willard, leading a team of people who provided Kerik with analyses of state data that purported to show fraudulent voting.

The Antrim report's key claims were immediately debunked, including by officials inside Trump's own Department of Homeland Security - but Trump allies, including Eastman, continued to repeat them.

On Jan. 8, Kerik billed the campaign for $66,371.54, including $55,295 on the rooms at the Willard from Dec. 18 to Jan. 8. The campaign reimbursed Kerik's firm on Feb. 9 for all but $120 of the total costs, campaign finance disclosures show.

On Feb. 2, the campaign made a $76,566.95 reimbursement payment for "recount: travel expenses" to Giuliani Security and Safety, a Giuliani firm, according to campaign finance disclosures.

The Washington Post's Alice Crites and Jon Swaine contributed to this report.