WASHINGTON — Nearly two years before he would begin his presidential campaign, Donald Trump arrived in Washington to show off his plans for a luxury hotel on Pennsylvania Avenue under a deal he had reached to lease the site from the General Services Administration.

But on that day in September 2013, he also had another property on his mind, only a block away in a prime location midway between the White House and the Capitol.

“What he wanted to talk to me about was the FBI project,” Dorothy Robyn, who at the time was the commissioner of the General Services Administration’s Public Buildings Service, said in an interview. “He was very interested in the FBI project. He was intrigued by it. He was excited by it.”

The FBI project was a long-debated plan to turn the Federal Bureau of Investigation’s crumbling Brutalist headquarters, the J. Edgar Hoover Building, over to a commercial developer, who could demolish it and build something new there. In return, the developer would construct a new, state-of-the-art campus for the FBI in the Washington area.

Trump never pursued it, but the FBI building continued to intersect with his business — and later with his presidency. As recently as early 2015, months before he announced his candidacy, an executive at his company expressed concern to a congressional aide about the redevelopment project creating potential competition for Trump’s hotel. And now, as the first real estate developer turned president, Trump has again taken an interest in the FBI project.

Within months of his taking office, his administration killed the original plan to trade the Hoover site for a suburban campus. A little over a year into Trump’s term, and after at least one meeting in which the president was personally involved, the administration announced a new plan that would keep the FBI on the existing site in a new building, rather than turn over the property for commercial development.

It is not clear that putting another commercial development on Pennsylvania Avenue, even one with a competing hotel, would necessarily hurt Trump’s hotel. Still, the degree to which Trump influenced decisions about the FBI building has emerged as the latest flashpoint in the running debate over whether his business holdings create conflicts of interest with his duties as president.

The sudden change in plans for the FBI project has already prompted an inspector general’s report that documented the president’s involvement in the process. And as Democrats make plans to investigate Trump more aggressively should they win control of the House in the midterm elections next month, they are zeroing in on the issue as one of their priorities and saying that the president should have recused himself entirely from any decisions about the building.

As an initial step, Rep. Elijah Cummings of Maryland, the top Democrat on the House Oversight Committee, and several other House Democrats are planning to send a letter to the General Services Administration seeking a trove of documents about the FBI project.

“It is Congress’ duty under the Constitution to make sure President Trump is serving the interests of the American people rather than his own financial bottom line,” Cummings said. “Republicans have failed to conduct basic, independent investigations of President Trump’s conflicts of interest, but this is exactly what the Constitution requires, and it is what Democrats will do if we are fortunate enough to be in the majority in November.”

The White House says Trump has merely followed the wishes of the FBI.

“The idea that the reason the president wanted the FBI headquarters to remain in its current location is based on anything other than the recommendation of the FBI is simply false,” said Lindsay Walters, a White House spokeswoman.

If nothing else, the story of Trump’s involvement with the FBI project is another example of how his pre-presidential career continues to bump up against his role as the government’s chief executive in ways that have raised questions about where one ends and the other begins.

— A Top Priority When Trump took office, the effort to build a new headquarters for the FBI had been underway for years.

A 2011 report by the Government Accountability Office cataloged the Hoover building’s woes. Opened in 1974, it was deteriorating, and netting had been installed to protect passers-by from falling debris. The building could fit barely half of the bureau’s headquarters staff, forcing the use of leased offices around the region. Its design, in an urban setting close to passing traffic, raised security concerns.

“A new consolidated FBI headquarters facility is urgently needed,” a top FBI official, Thomas J. Harrington, said at the time.

In late 2012, the General Services Administration, which handles real estate for the federal government, began seeking ideas from developers about building a new headquarters while turning over the Hoover site for redevelopment. That move started what would become a multiyear undertaking that eventually focused on potential sites in Greenbelt, Maryland; Landover, Maryland; and Springfield, Virginia.

In the years leading up to his presidential campaign, Trump was himself doing business with the General Services Administration. In 2013, his company, the Trump Organization, reached a deal with the agency to turn the Old Post Office building on Pennsylvania Avenue into what became the Trump International Hotel, now a favored dining and drinking spot for Republicans in Washington and sometimes the hotel of choice for visiting foreign officials.

In early 2015, with the Trump hotel project underway, a Trump Organization executive suggested there was unease within the company over the threat of possible competition from the FBI project, a Democratic congressional aide said.

The executive, David Orowitz, expressed concerns about what could be built on the Hoover site if it were redeveloped, according to the aide, who spoke on the condition of anonymity to discuss a private conversation.

Orowitz was worried that new competition from across Pennsylvania Avenue could imperil the business prospects of the Trump hotel, and he asked the aide for assistance in restricting what could be built on the FBI site, the aide said.

The aide recalled that no action was taken on Capitol Hill to help. Orowitz, who has since left the Trump Organization, declined to comment.

A spokeswoman for the National Capital Planning Commission, which drafted guidelines for the redevelopment of the Hoover site, said the Trump Organization never contacted the commission regarding the property. The final guidelines called for a mixed-use development; a hotel was listed as among the possible uses that were encouraged.

By the time Trump took office, in January 2017, the Trump International Hotel was open, and the General Services Administration appeared poised to pick a site and a developer for the new FBI headquarters in the Washington suburbs.

But that July, the agency made an unexpected announcement: It was scrapping the project because of insufficient funding. The project had been a complicated venture with an unusual structure for a federal real estate deal, in which the developer of the new FBI campus would receive the Hoover building in exchange.

In effect, the Hoover site would be a portion of the developer’s compensation for building the new FBI campus. But the swap came with a catch: The developer would have to wait years to take possession of that prominent Pennsylvania Avenue site because the new campus would have to be built first.

“Clearly the swap exchange was a difficult maneuver, a situation where many pieces had to fall into place,” David Wise, an official at the Government Accountability Office, said at a Senate hearing after the project was canceled. “It was kind of a complicated mosaic of effort, and it just didn’t really work out.”

This February, the Senate Environment and Public Works Committee received a new plan from the Trump administration: Instead of building a suburban campus, the government would demolish the current headquarters and build a new one for the FBI on the existing site.

Remaining in that location would keep the bureau close to the Justice Department, whose headquarters is across the street.

“We were stunned,” said David S. Iannucci, an economic development official for Prince George’s County, Maryland, which was home to two of the three suburban sites in the running for the campus. “It didn’t compute. It just literally didn’t make any sense.”

— Meetings at the White House

The abrupt change did not go over well with lawmakers from Maryland and Virginia whose states had been eager for the new headquarters.

Rep. Gerald E. Connolly, D-Va., asked the inspector general for the General Services Administration to investigate.

Last month, six Democratic senators asked the Justice Department’s inspector general to conduct an investigation, and a group of House Democrats also made a request for an inquiry. A spokesman for the Justice Department’s inspector general declined to comment.

When Emily W. Murphy, the administrator of the General Services Administration, appeared in April before a House subcommittee, she dodged questions about whether Trump or anyone at the White House had been involved in the discussions about the FBI headquarters.

Murphy, a Trump appointee, said the FBI had wanted to “put the J. Edgar Hoover site back into play,” and requested that her agency consider renovating the existing headquarters. Her agency did not like that idea, so it suggested demolishing the building and constructing a new headquarters on the site instead.

In fact, the White House had been involved, at least between the decision to kill the original project and the announcement of the new plan, according to the review by the General Services Administration’s Office of Inspector General in response to Connolly’s request.

In December 2017, five months after the decision to cancel the original project, Murphy and another official from her agency met with the White House chief of staff, John Kelly, and the budget director, Mick Mulvaney, about the FBI headquarters.

In January, she met at the White House with Kelly and Mulvaney, along with Rod Rosenstein, the deputy attorney general, and Christopher Wray, the FBI director. Then the group met with Trump in the Oval Office.

Precisely what transpired in that meeting is unclear. But according to the inspector general’s report, an official at the General Services Administration sent an email a few days later that referred to “what POTUS directed everyone to do” and “POTUS’ orders.” Another official from the agency wrote in an email about delivering “the project the president wants on the timetable he wants it done.”

Trump made clear over several months that he wanted to be involved with the FBI project, two former Trump administration officials said. The president could not understand, they said, why people wanted to relocate the bureau’s headquarters to Maryland or Virginia. Among his concerns was that the FBI was giving up what one of the former officials called “an iconic address.” Trump told Kelly that he had a strong personal interest in the project and would take opportunities to weigh in on it, the former officials said.

Trump is not a fan of the building that stands there now. The website Axios reported this summer that Trump was “obsessed” with the Hoover building and considered it “one of the ugliest buildings” in Washington. People who have talked with Trump about the building confirmed that he thinks it is ugly.

A few weeks after the Oval Office meeting, the Trump administration presented the Senate environment committee with its plan to keep the FBI on Pennsylvania Avenue — a course of action that would keep that property out of the hands of a commercial developer.

Murphy attended another meeting with Trump about the FBI project in June, according to the inspector general’s report, which was released in August.

In Senate testimony after the new plan had been announced, an FBI official described the choice to stay on the Hoover site as “an FBI decision.” A spokeswoman for the bureau declined to comment for this article. Lawyers for Murphy told the inspector general that the FBI had made that decision “well before” Murphy met Trump. — Lingering Questions

Trump’s handling of his business interests as president has already led to court cases. Last month, a federal judge in Washington said a group of congressional Democrats could move ahead with a lawsuit contending that Trump’s continued ownership of his hotel and other businesses violates the Constitution’s ban on a president accepting payments and other benefits from foreign governments. A federal judge in Maryland allowed a similar lawsuit to move forward this summer.

One lingering question is what exactly the president said in his meetings with Murphy and other officials. The White House told Murphy that she was “not authorized to disclose the content of presidential communications from those meetings,” the General Services Administration’s chief of staff, Robert Borden, wrote in a memo to the inspector general, Carol F. Ochoa.

This spring, Murphy went into the House hearing with the intention of keeping quiet about the president’s involvement.

She told the inspector general’s office that she anticipated being asked if the White House had been involved in the FBI project, and that the participants in her preparation sessions for her testimony agreed that she should try to respond “without specifically addressing the White House meetings,” according to the inspector general’s report.

The lawmaker who questioned her at the hearing, Rep. Mike Quigley, D-Ill., said in an interview that he believes Murphy misled him and his colleagues.

He said he is eager to question her further: “What was said in those meetings?”