This article has been updated.

House Speaker Nancy Pelosi (D-Calif.) has not exactly embraced the idea of launching an impeachment inquiry into President Trump. The political calculus is fairly obvious: She managed to wrench control of her chamber from the opposition in November, and she’s wary about anything that might send her caucus back to the minority. As was made clear this week, her opposition to a formal impeachment became untenable in the face of the new questions about Trump’s interactions with the president of Ukraine and with increasing agitation in the active Democratic base to take some sort of action.

Given that reluctance, Pelosi has established guidelines for the inquiry meant to keep it from sprawling too broadly. The Washington Post’s Mike DeBonis and Rachael Bade reported on Thursday that Pelosi was eager to wrap up investigations in a matter of weeks to hold a vote on impeachment before the holidays. House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) — whose committee is leading the effort — told CNN that hearings would be held as early as next week, putting Democrats on track for a vote before Thanksgiving.

Students of the process or those who were paying attention to the news in the late 1990s understand how this process works. The House considers articles of impeachment against the president (in this case). If approved, the Senate then considers whether to remove the president from office. In 1999, the Senate held a trial in which evidence against President Bill Clinton was considered. While impeached by the House, Clinton was ultimately acquitted by the Senate and, therefore, not removed from office.

Part of Pelosi’s hesitation in launching this process is that impeachment isn’t overwhelmingly popular. Advocates of the process argue that by initiating an inquiry, by digging into what’s known in public and unearthing new evidence through the use of subpoenas, public opinion will shift against Trump as it did against Richard Nixon in 1974. A shift against Trump means, generally speaking, a shift to the Democrats’ advantage.

The merits of that Nixon analogy not withstanding, there’s a more problematic consideration. The faster the House moves on impeachment, the less time it has to dig into the allegations and, therefore, to uncover the sort of evidence that might change those minds.

Well, one might argue, isn’t that a better function of the trial in the Senate anyway? Let the impeachment articles serve as an indictment and let the Senate act like a criminal court. Which brings us to a central stumbling block in the impeachment effort: Senate Majority Leader Mitch McConnell (R-Ky.).

House Democrats began a formal impeachment inquiry of President Trump on Sept. 24. Here's how the impeachment process works. (Peter W. Stevenson/The Washington Post)

There exist Senate rules of procedure that dictate how impeachment trials should be run. As Michael Dorf, Robert S. Stevens professor of law at Cornell Law School, put it in an email to The Post, the rules include a “a lot of ‘shall’ language” — language that gives McConnell and the Republican majority a lot of flexibility in how they conduct a trial.

Or whether they conduct a trial at all.

“Some people read the Constitution’s language that the Senate ‘shall have the sole power to try impeachments’ to be a mandate, requiring the Senate to conduct a trial based on the articles of impeachment approved in the House,” explained Michael Gerhardt, Burton Craige distinguished professor of jurisprudence at the University of North Carolina School of Law. “In practice, the Senate has always felt obliged to do something when it formally received impeachment articles from the House, including holding a streamlined process for President Clinton when it was apparent conviction and removal were highly unlikely.”

“As a practical matter,” he continued over email, “the Majority Leader will have substantial discretion on the process, if any, he fashions in response to the articles.”

“If any.” In other words, impeachment trials are themselves one of those “what the norms dictate” activities of the Senate. McConnell could simply decide against holding a trial at all. Nothing goes on television. No more evidence comes to light. From a majority leader who simply declined to hold a vote on a presidential Supreme Court nominee, it’s far from inconceivable.

Gerhardt added: “If he has the Senate do nothing, that would be unprecedented — the Senate has always done something in response, even when a majority thought the Senate lacked jurisdiction (because the official resigned in the interim) or thought a conviction was impossible.”

Louis Michael Seidman, Carmack Waterhouse professor of constitutional law at Georgetown Law, pointed to existing precedent on the subject.

“In United States v. Nixon (remarkably, this is Walter Nixon, a federal judge who was impeached, not Richard Nixon — Nixon is a bad name to have if you want to avoid impeachment) the Supreme Court held that the nature of a ‘trial’ for impeachment purposes was a political question not amenable to judicial resolution,” Seidman wrote in an email.

The question “is not legal but political,” Seidman continued. “The real issue is whether McConnell could get away with this. That depends on where public opinion is when the issue comes up” — meaning, perhaps, how effective Democrats have been at swaying Americans with what they find.

“As a matter of constitutional morality, I think that McConnell has a duty to hold a trial,” Seidman added, “but enforcement of that duty will have to come from the outrage of the American people if, in fact, they are outraged.”

In an interview with NPR in March, McConnell said the Senate had “no choice” and that the Senate “immediately goes into a trial.” At that point, though, he was talking about a hypothetical, not a specific charge coming from the opposition. Nor did he delineate how robust any such trial might be.

Update: In an interview with CNBC on Monday, McConnell reiterated that he would “have no choice but to take it up.” He added an important caveat, though: “How long you are on it is a different matter.”

House Democrats are fully within their rights to determine the extent and thoroughness of their impeachment inquiry. If articles of impeachment pass without significant evidence being presented to the public and without public opinion shifting in favor of moving forward with a trial, it’s easy to imagine McConnell simply declaring the entire thing to be unjustified, unfair and unnecessary, and either skipping a trial or moving quickly to a vote.

“There’s nothing ‘mandating’ a trial if by that you mean that no external power (the Supreme Court) is going to enforce the mandate,” Seidman wrote. Once the articles of impeachment leave the House, the rest is up to McConnell.