Just as the House Intelligence Committee ran out of scheduled hearings, and it seemed clear that not a single Republican would vote for impeachment, another shoe has dropped: Monday’s ruling to compel congressional testimony from former White House Counsel Don McGahn looks to be a game-changer, leading McGahn to spill the beans on Donald Trump, and possibly compelling other Executive Branch members to testify before the House.

The White House will appeal of course, but if the ruling is upheld, it’s huge. Why does McGahn matter? According to the Mueller Report (and based on interviews with McGahn and others), Trump directed McGahn to call Deputy Attorney General Rod Rosenstein to “have the special counsel removed.”

McGahn refused to comply—one of the many examples in which subordinates potentially saved the president from an obstruction of justice charge. Few people actually read the Mueller Report, of course, and if McGahn says in public, on national TV, what he apparently said to Mueller’s investigators, Trump’s public support could drop substantially, and it could lock in an obstruction count in whatever articles the House draws up.

But that’s not even the biggest potential problem McGahn’s testimony could pose for Trump.

Testimony from Roger Stone’s trial raised new questions regarding whether Trump lied in his written deposition to Mueller concerning whether he ever discussed WikiLeaks with Stone.

Being caught lying to Mueller would, of course, be a very big deal. Don’t forget, Bill Clinton wasn’t brought down because of sex, but because of perjury. Michael Flynn was convicted of lying to the FBI. One of the charges Stone was convicted of was lying to Congress. If McGahn has to go up to the Hill and—under oath—answer whether the president lied or instructed him to lie in that written testimony, it would be a bombshell moment. And if McGahn were to testify that Trump did, in fact, lie to Mueller, that could be (I’m going to sound insane here, I know) enough to cause some Republican attrition.

As this all suggests Monday’s court decision might—MIGHT—end up being one of the most underrated developments of this saga.

But it’s not just about McGahn.

An equally consequential outcome of this court ruling could be that it makes it more likely that other top Executive Branch members—possibly including former National Security Adviser John Bolton—will testify.

This might still be a long shot, but it’s not entirely crazy. In early November, Bolton’s lawyer sent a letter to the House saying his client “was personally involved in many of the events, meetings, and conversations about which you have already received testimony, as well as many relevant meetings and conversations that have not yet been discussed in the testimonies thus far.”

Why would Bolton’s lawyer tease us like that? There seem to be two possible answers: Either Bolton is craving media attention, or he is looking for an excuse that would permit him to overcome the executive-privilege objections. If it’s the latter, the McGahn decision—which will surely be appealed—could at least provide a cover rationale.

Another rationale for Bolton to comply with his subpoena: During her testimony, Fiona Hill might have provided such an excuse when she alleged that EU Ambassador Gordon Sondland “was being involved in a domestic political errand” while she was “involved in a national-security foreign policy. And those two things had just diverged.”

“ We are now looking at the possibility of a pincer move on Trump, involving McGahn and Bolton. ”

This could potentially open the door for senior aides like Bolton (and Rudy Giuliani, Mike Pompeo, and Mick Mulvaney) to remain exempt from discussing national-security issues, while also being compelled to discuss this “domestic political errand,” which “diverged.”

Regardless of how this plays out, Monday’s court ruling reinforces a point I’ve been making to the naysayers who believe impeachment is a fool’s errand. Once you start subpoenaing witnesses and accruing on-the-record testimony, it’s impossible to predict how one development might lead to another (just as testimony in the Stone trial might now play a major role in the impeachment inquiry).

Additionally, sometimes, once you start the process, you get lucky. In this instance, however, Republicans seem to have drawn the short straw with Judge Ketanji Brown Jackson, an Obama appointee, whose questions during oral arguments last month seemed to signal she would rule in favor of the House.

We are now looking at the possibility of a pincer move on Trump, involving McGahn and Bolton: The former gets him on lying, the latter on trying to rig the next election. If that happens, Trump’s political future is over. It might be time to start heading to the bunker.