When we talk about the threat of Donald Trump using the presidency for his own monetary gain — something we thought we’d never have to worry about again since no president of either party would even consider doing so — what exactly do we mean?

If you're less than clear, I have a story that illustrates quite well the unique threat of corruption that Trump poses.

It has to do with the FBI, specifically the dilapidated headquarters it currently occupies in downtown Washington. To begin, here's the latest news, as reported by The Washington Post:

"The Justice Department's inspector general will investigate the FBI's role in dropping plans a decade in the making to move its headquarters to the Washington suburbs, he told Congress in a letter Tuesday.

"The inspector general, Michael Horowitz, told House committee leaders that he is initiating a review of actions at the DOJ and FBI that led to the canceling of the plans in favor of building a smaller replacement for the J. Edgar Hoover Building downtown and dispersing other FBI staff elsewhere.

"The review could produce new revelations about the Trump administration's stunning reversal of bipartisan plans for the development of a new, highly secure campus that would have gotten the bureau out of the fast-deteriorating Hoover building."

You will not be surprised to learn that Democrats' efforts to conduct oversight on this matter have been met with stonewalling from the administration.

So what does this have to do with Donald Trump's financial interests? Let me lay out the basic story.

As it became obvious that the FBI had to get the heck out of the Hoover Building, years of study and analysis and negotiation between the FBI, the General Services Administration (the federal agency that oversees land and buildings) and Congress led to the conclusion that the best option was for the bureau to move out to the suburbs.

There, they could have a larger space, which they needed, and more easily establish security than they could in the middle of a bustling city (the suburbs in Maryland and Virginia are full of headquarters for federal agencies, including the Department of Defense, the CIA, the NIH, and many others).

It was all pretty much decided — until Trump took office. The key fact you have to know to understand what happened next is that the Hoover Building is located at Pennsylvania Avenue and 10th Street NW. The Trump International Hotel is located at Pennsylvania Avenue and 11th Street NW.

Once the FBI moved to the suburbs, the GSA would then be able to level the Hoover Building and lease out that highly desirable piece of property to another tenant. Like, say, a hotel that would compete with the Trump International. Or some kind of building with restaurants that would compete with the restaurants in the Trump International.

So the president, in a move that was highly unusual to say the least, got personally involved in the question of where the FBI was going to move. Reports described him as "obsessed" with the building, frequently raising it with members of Congress.

The Trump administration then came up with its own plan: Instead of moving out to the suburbs, the bureau would move twice — first into temporary headquarters, which it would occupy while the Hoover Building was demolished and a new building erected in its place, and then back into the new building on the same location.

As The Post reported last year, the administration's plan "stunned FBI experts and members of Congress. The GSA and FBI spent several years, thousands of hours of staff time and millions of dollars securing approvals for sites in Greenbelt and Landover, in the Maryland suburbs, and in Springfield, Virginia."

In addition, a previous inspector general report concluded that the head of the GSA misled Congress when she used a bit of clever non-answering to fool them into thinking that Trump had no involvement in the decision-making on the project, when in fact she had personally discussed it with him.

So what are we left with? The Trump administration's story is that the president's unusual involvement with this project has nothing to do with concerns about competition with his hotel, but is a result only of his interest in real estate and his insistence that taxpayer funds be spent wisely (even though his plan will almost certainly cost much more than the original plan).

If you believe that, you probably also believe that the administration wanted to add a citizenship question to the Census because they were so concerned about properly enforcing the Voting Rights Act.

Unfortunately, there is probably no smoking-gun piece of evidence that will prove what Trump is up to. Everyone knows it's perfectly plausible that he's making decisions affecting thousands of personnel, billions of dollars, and the national security of the United States based on whether he can make a few million more bucks from his hotel. The FBI knows it, the GSA knows it, Congress knows it — everyone.

Perhaps the inspector general report will bring new evidence to light, making it impossible to deny that. Even if that happens, the administration will insist it doesn’t matter, and in one sense they’ll be right. This is just how things work in Trump’s Washington, and we’re all supposed to accept it.