A few days after President Biden’s inauguration put to rest one of the most chaotic transitions in U.S. history, a former Army colonel with a background in information warfare appeared on a Christian conservative podcast and offered a detailed account of his monthslong effort to challenge the validity of the 2020 vote count.

In a pleasant Texas drawl, the former officer, Phil Waldron, told the hosts a story that was almost inconceivable: how a cabal of bad actors, including Chinese Communist officials, international shell companies and the financier George Soros, had quietly conspired to hack into U.S. voting machines in a “globalist/socialist” plot to steal the election.

In normal times, a tale like that — full of wild and baseless claims — might have been dismissed as the overheated rantings of a conspiracy theorist. But the postelection period was not normal, providing all sorts of fringe players an opportunity to find an audience in the White House.

Mr. Waldron stands as a case study. Working in conjunction with allies of President Donald J. Trump like Rudolph W. Giuliani, Sidney Powell and Representative Louie Gohmert of Texas, a member of the ultraconservative House Freedom Caucus — and in tandem with others like Michael T. Flynn, Mr. Trump’s first national security adviser and a retired lieutenant general — Mr. Waldron managed to get a hearing for elements of his story in the very center of power in Washington.

Last week, the House committee investigating the events of Jan. 6 issued a subpoena to Mr. Waldron, saying that it wanted to know more about his role in circulating an explosive PowerPoint presentation on Capitol Hill and to Mark Meadows, Mr. Trump’s last chief of staff.

The presentation, which Mr. Meadows gave to the committee (and which he said he never acted on), counseled Mr. Trump to declare a national emergency and to invalidate all digital votes in a bid to stay in power — the same advice that other election deniers gave him at the time.

Committee officials have given Mr. Waldron, who retired from the military in 2016 and now owns a bar in Central Texas, until Jan. 10 to turn over any relevant documents. They have also tentatively set a deposition for the week after.

When The New York Times sent a reporter last week to Mr. Waldron’s bar, outside of Austin, he told the reporter to leave his property immediately. He then called the local sheriff and described the reporter’s car, adding that the reporter was slurring his words and seemed impaired.

It remains unclear whether Mr. Waldron will cooperate with the House committee. But the account he gave in January to the podcast, Flyover Conservatives, and in recent news articles, may give investigators plenty to work with.

Mr. Waldron opened his story by saying that his “research” into the 2020 election began that summer, when he started to examine what he described as a network of nonprofit groups connected to Mr. Soros, an outspoken supporter of liberal causes who has long been at the center of right-wing, often antisemitic conspiracies.

Around that time, Mr. Waldron said, he and his associates — whom he has never named — developed a relationship with a Texas cybersecurity company, Allied Security Operations Group, which was co-founded by a man named Russell J. Ramsland Jr.

According to Mr. Waldron, Mr. Ramsland and his team had made a startling discovery: that the Chinese Communist Party, through software companies it controlled, had developed a way to flip votes on American tabulation machines, particularly those built by Dominion Voting Systems. (Dominion has adamantly denied its machines have security flaws and has filed defamation suits against some of those who have repeated the claims, including Fox News, Mr. Giuliani and Ms. Powell.)

Beginning in August last year, months before Election Day, Mr. Waldron started to “raise an alarm,” as he put it, and tried to get anyone he could interested in his claim that the country’s voting machines were susceptible to hacking.

He told the podcast hosts that he and his partners had reached out to officials in the Department of Homeland Security, the Office of the Director of National Intelligence and the Cybersecurity and Infrastructure Security Agency, all of which were run by Trump appointees at the time. Mr. Waldron said he also sent an email to Mr. Trump’s director of strategic communications, but all of it “fell on deaf ears.”

But there was one person who listened, Mr. Waldron said: Mr. Gohmert, the Texas Republican and a member of the House Freedom Caucus, a group that was traditionally loyal to Mr. Trump and ultimately played an outsize role in his efforts to overturn the election. By Mr. Waldron’s account, Mr. Gohmert promised to pass along his concerns about voting machines to the president, but apparently failed to do so until after the election. (Mr. Gohmert did not respond to questions seeking comment.)

Once the votes were cast and Mr. Trump was declared the loser, Mr. Waldron embarked on what amounted to a two-pronged assault on the election. First, with Mr. Ramsland’s company, Allied Security, he funneled information about supposedly suspicious spikes in votes and other dirt on Dominion Voting Systems to Ms. Powell, a pro-Trump lawyer who filed four unsuccessful lawsuits accusing Dominion of a conspiracy to hack the election.

According to court papers filed by Dominion, Mr. Ramsland was hired that summer by Patrick M. Byrne, the former chief executive of Overstock.com and a Trump supporter, to “reverse engineer” the evidence needed to “mislead people into believing” that the 2020 election had been rigged.

When the legal challenges failed, Mr. Waldron took a new tack. He partnered with Mr. Giuliani, who was spearheading Mr. Trump’s attack on the election, and joined him at a series of unofficial election fraud hearings conducted by lawmakers in a handful of swing states. Mr. Giuliani did not respond to questions seeking comment on Mr. Waldron, but he has testified in a defamation lawsuit filed by Dominion that he not only knew and admired Mr. Waldron, but also had “substantial dealings” with him.

Even as he toured the country with Mr. Giuliani, Mr. Waldron appeared to have been working on a third attack on the election results: assembling the 38-slide PowerPoint presentation that ended up in Mr. Meadows’s possession. In his podcast interview, Mr. Waldron said that he and his associates had managed to get a nascent version of the proposal — to declare a national emergency and use the crisis to order a recount of paper ballots in eight key counties — to Mr. Trump around Thanksgiving, far earlier than public accounts had suggested.

On the podcast, Mr. Waldron said that he and his team had promised Mr. Trump that they could get preliminary results of the paper recount in 10 days and have final results in a month.

“We gave the president these solutions over time, some as early as before Thanksgiving and some all the way up toward the end of the process,” Mr. Waldron said.

As for how Mr. Trump might go about declaring a national emergency, Mr. Waldron told the podcast that the gambit hinged on a report about foreign interference in the election that John Ratcliffe, the director of national intelligence at the time, was bound by congressional mandate to present by Dec. 18. If Mr. Ratcliffe pointed a finger at China, accusing Communist Party officials of having manipulated votes in the United States, Mr. Waldron said, Mr. Trump would be within in his rights to declare an emergency and seize some voting machines to conduct a paper recount.

Similar advice was being given to the president by others.

In mid-December last year, for instance, Mr. Flynn appeared on Newsmax, the right-wing television channel, and pushed the president to impose martial law and use the military to “rerun” the election.

In a dramatic meeting in the Oval Office, Mr. Flynn, Ms. Powell and Mr. Byrne urged Mr. Trump to use an emergency declaration to demand a recount of votes in key states on live TV or have the National Guard redo those states’ elections, Mr. Byrne wrote in his book, “The Deep Rig.”

Mr. Waldron has claimed that he worked under Mr. Flynn at the Defense Intelligence Agency, but the Army declined to comment, saying it could discuss only “releasable” details of Mr. Waldron’s military career. Mr. Flynn did not respond to messages seeking comment.

Another person pushing Mr. Trump to impose martial law was Stewart Rhodes, the leader of the Oath Keepers militia. At a pro-Trump “Stop the Steal” rally in Washington on Dec. 12, Mr. Rhodes and members of his group provided security for Mr. Flynn, who was speaking at the event. Helping the Oath Keepers, Mr. Rhodes said, was a shadowy group of former Special Forces operators called the First Amendment Praetorian. (Their leader, Robert Patrick Lewis, has also been subpoenaed by the House committee.)

During the rally in December, Mr. Rhodes gave a television interview in he which he railed against China and urged Mr. Trump to fight against “traitors” at home. “He should drop the hammer with the Insurrection Act and wage war on the insurrection that’s going on in our country,” Mr. Rhodes said.

In the end, Mr. Ratcliffe did not meet his Dec. 18 deadline to publish the report on foreign interference. Speaking on the podcast, Mr. Waldron blamed Mr. Ratcliffe’s failure on rogue elements in the intelligence community, still loyal to former President Barack Obama, who “actively downplayed the role of China in the elections.”

By that point, Mr. Trump had turned his attention to another matter: a new rally he had scheduled in Washington for Jan. 6, the day that Congress would make its final certification of the electoral vote.

In the run-up to the president’s event, Mr. Waldron was busy. He told The Times this month that on Jan. 4, members of his team spoke to a group of senators about allegations of election fraud contained in the PowerPoint presentation that recommended declaring a national emergency. The next day, Mr. Waldron said, he personally briefed a small group of House members on the same proposal.

One day later, a mob stormed the Capitol. It remains unclear where Mr. Waldron was that day.

David Montgomery contributed reporting.