In the past 20 years, Americans have been presented with more than 1,100 episodes of “Law & Order” and its spinoffs but only two presidential impeachments. We are well versed in the “two separate but equally important groups” that put criminals in jail: the police investigators and the prosecutors who ensure their convictions. So it’s hard not to map that process onto what’s underway on Capitol Hill.

Following the “Law & Order” framework, the House is conducting an investigation that may result in impeachment — the grand jury returning an indictment. Then it’s off to the Senate for a trial and, potentially, conviction. Neat and tidy — and, certainly, useful when considering the process-based complaints being made by President Trump’s allies. Grand juries don’t operate in public or involve input from attorneys for the accused, one line of argument goes, so why should the House investigation?

As with everything in Washington, though, it's not that simple.

Few people are as well-versed in the process of investigating a president than former White House counsel John W. Dean. Dean served President Richard Nixon until 1973, when he decided to instead aid investigators in the Watergate scandal. In detailed public testimony, Dean revealed his involvement in Nixon’s efforts to undermine his political opponents and the investigation into his activities. But Dean’s testimony didn’t start that way.

“What’s interesting is that the prior modern impeachment proceedings have all been initiated in private and in closed proceedings, unlike they’re claiming they should be now,” Dean told The Washington Post this week. “The Nixon proceeding was done — the stuff that really counted was all done in a grand jury. Before the Senate Watergate Committee and public hearings, they had closed hearings. They had executive session hearings.”

“My own testimony, I spent, I don’t know, maybe six, eight, 10 weeks with Sam [Dash] going over it in private,” Dean said, referring to the chief counsel for the Senate committee investigating Watergate, chaired by then-Sen. Sam Ervin (D-N.C.). “There, only Sam Ervin and Sam Dash were the only ones that — I was unwilling to do the norm because I said, listen, if you get this out and in circulation, they will be dragging bushes everywhere. It will all disappear. I said I just am not willing to do it. So we did it on that arrangement.”

This, of course, is a key reason grand jury proceedings and criminal investigations are similarly kept under wraps, or, to use another salient example, Attorney General William P. Barr’s probe into the origins of the Russia investigation.

Over the course of the conversation with Dean, though, the gaps in the criminal investigation analogy to impeachment became increasingly apparent. For one thing, the Senate trial isn’t really what we would think of as a trial. As Dean pointed out, it’s more like a bench trial, with the Senate acting as both judge and jury — in a process where it can also make up new rules as it goes along.

There are guidelines for how things should progress in the Senate. Dean pointed to a 1986 memo detailing procedures for impeachment trials in the Senate, written in part by the then-Senate parliamentarian Robert Dove. But the memo also “shows that the Senate drafts its own rules as it goes along, typically, and there’s a lot of flexibility,” Dean said. That’s important to consider when assessing the current process complaints. If the House votes to impeach Trump, the process and trial are then in the Republican-controlled Senate’s hands.

The analogy to the criminal process is useful, particularly at this early stage, Dean said, but it “barely” applies as a guide to what to expect because of the flexibility the Senate has.

“A criminal trial is so highly structured, and not following the procedure for a criminal trial is cause for a mistrial. And that can result in either dismissal or a retrial,” he said. “Whereas impeachment, that isn’t going to happen.”

That also means that objections to process based on expectations from criminal trials are often unfounded. Consider “due process,” a complaint central to Republican objections to the current inquiry. The impeachment clause in the Constitution doesn't include any due process stipulations; in fact, due process in the criminal system wasn't added until amendments to the Constitution were ratified. (This might flummox Republicans who insist upon constitutional originalism, Dean pointed out.)

It’s not because impeachment was an abstract concept to the drafters of the Constitution. Shortly before the Constitutional Convention began in 1787, the British governor general of India, Warren Hastings, had been arrested and brought to Parliament to face the legislative proceeding of impeachment. Hastings was cleared eight years later.

In Dean’s estimation, the existing House inquiry is perhaps too open.

“It helps the targets” to have public awareness of the evidence being gathered, he said. “That was one of the articles of impeachment for Nixon, who was pumping the head of the criminal division, Henry Peterson, about what the grand jury was doing. And then he was turning around and feeding that grand jury information to [his aides H.R.] Haldeman and [John] Ehrlichman so they could deal with it. And that became part of one of the abuses of process for him. There is a reason to do these things in closed sessions."

The hearings that have been conducted by the House have included a number of Republicans, including staunch Trump allies like Reps. Lee Zeldin (N.Y.) and Devin Nunes (Calif.). As Republicans publicly complain about a lack of access, Dean argued that it was extremely unlikely that Trump’s team was in the dark.

“I’m just confident that Trump has a back channel to the Republicans who are on one of those committees,” Dean said. “He’s got a back channel into that. He knows exactly — they’re making copious notes, and they’re coming out, and somebody is telling the White House counsel or somebody in the White House exactly what’s going on.”

The implication of such a back channel? That Trump and his allies could, if desired, work to bury or undermine incriminating information.

Probably the most important thing to remember about the impeachment process is that it is fundamentally political. The complaints from Trump and his allies are heavily about securing political support. Some House Democrats are similarly trying to move public opinion with leaks about what’s being discussed behind closed doors.

Dean made clear the importance of politics in the impeachment fight. He described being in Washington during the impeachment of President Bill Clinton in the late 1990s.

“I can’t say how many people, Republicans who had no idea where I was coming from — I wasn’t coming from anyplace in particular — who said, ‘This is get-even for Nixon,’ ” he said.

Intrigue worthy of “Law & Order.”