The revelation that the FBI opened a counterintelligence investigation to determine whether President Donald Trump is compromised by or working for the Russian government is beyond disturbing. To deepen the unease, another report disclosed that Trump went to “extraordinary lengths” to conceal what he discussed with Russian President Vladimir Putin.

The unsettling news should concern all Americans. But, as we await the discoveries of special counsel Robert Mueller, we must distinguish between a counterintelligence nightmare and a criminal violation.

It is possible that Trump was compromised by the Russians but that there is insufficient evidence to prove that he committed a crime resembling what the public has been calling “collusion.” The recent revelations, moreover, may have changed our understanding of “collusion” as well as another word we’ve heard a lot of since Mueller started his investigation: “obstruction.”

To put it mildly, it is highly unusual to be discussing a sitting president’s possibly being compromised by a country commonly seen as an enemy. Being compromised by the Russians is not a crime in and of itself, though it could cause someone to commit any number of crimes. Trump’s being compromised might, for instance, have caused him to lie under penalty of perjury, to trade official acts in exchange for something of value, or to accept foreign contributions in connection with an election.

It’s true, though, that we appear to be closer to prosecutors’ making a case that a key Trump associate committed a crime resembling collusion. The recent revelation that former Trump campaign chair Paul Manafort shared the Trump campaign’s private polling data with alleged Russian intelligence operative Konstantin Kilimnik was the most important evidence of potential “collusion” revealed publicly thus far.

This evidence strongly suggests that Manafort sought aid from the Kremlin. Why else would the campaign chair of a major party presidential candidate provide internal polling data to a Russian intelligence operative? While it is not illegal in and of itself to prove internal polling data to a Russian operative, neither is wearing a ski mask while walking into a bank.

Both actions strongly suggest a crime was committed.

The most obvious potential liability for Manafort stems from Mueller’s indictment of Russian operatives for defrauding the United States by “interfering with the U.S. political and electoral processes, including the presidential election of 2016.” To prove that Manafort committed a crime, as in any conspiracy charge, Mueller would need to prove that Manafort knew of the criminal conspiracy and helped make it succeed. So far, there’s no public evidence that proves Manafort’s knowledge.

Still, Mueller knows far more than we do, and it’s very possible he can prove that Manafort committed a crime when he provided polling data to Kilimnik. Yet even proof that Manafort committed a crime resembling “collusion” would not prove that Trump was implicated in the crime.

But with the new revelations about Trump, that matters much less than it did even last week. We now know that the FBI counterintelligence investigation into Trump began with events surrounding the firing of FBI Director James Comey.

In that context, obstruction takes on a different, graver meaning. You might say it takes on the same meaning as collusion. And if Mueller can prove that Trump obstructed justice, does it even matter whether he can prove that Trump committed other crimes? After all, the FBI saw Trump’s attempt to obstruct the FBI investigation by firing Comey as evidence that Trump was trying to aid Russia by undermining the investigation of Russian efforts to interfere with our election. The FBI saw Trump’s obstruction as a form of “collusion,” aiding the Russian government by undermining our own.

Even based on public knowledge, the obstruction case against the president is very strong. It’s so strong, in fact, that even a year ago, I concluded that Mueller would find that Trump obstructed justice. Since then, the evidence against Trump has grown, as Trump has publicly revealed his desire to obstruct justice on multiple occasions. On its own, the evidence will establish that Trump obstructed justice. Even Trump’s ardent defenders, like Trump attorney Rudy Giuliani or Professor Alan Dershowitz, argue that Trump couldn’t obstruct justice as a technical legal matter. They don’t argue that the facts won’t show he tried to do so, because they can’t.

But Mueller is extremely unlikely to indict Trump for obstructing justice, because the Justice Department has determined that a sitting president can’t be indicted. What really matters, then, is whether Trump committed “high crimes and misdemeanors” worthy of impeachment. If Mueller proves that Trump obstructed the FBI and Justice Department investigation into the Russian attack on our democracy because he was compromised by the Kremlin, would that be worthy of impeachment? It should be, but that’s a question for the American people—through their elected representatives in Congress—to decide.