Years ago, my father shared a piece of wisdom, learned from decades of running the cash register at a small store. He would ring up the purchases, take the money from the customer, and hand them the change. Now, he was teaching me how to do it.

The toughest problem, Dad said, was not customers cheating. That seldom happened in our small town, where everybody knew each other. No, the toughest problem was when your customer sincerely thought she gave you a $20 and you, with equal sincerity, thought she gave you a $10. That’s hard to resolve and leave everyone satisfied. Very hard.

It’s also a metaphor for today’s political crisis. Each side sincerely, truly believes it is defending the basic values of American constitutional democracy, while the other side is trying to undermine them. We have not seen anything like it since the 1970s when this country faced the twin crucibles of Vietnam and the Watergate scandal.

To compound the current crisis, the conflict over Donald Trump, U.S. spying, and Russian political meddling builds on already-deep divisions in America. It’s not just a divided Congress, where only one Republican senator has a voting record that overlaps with one Democrat (Susan Collins, a Maine Republican, and Joe Manchin, a West Virginia Democrat).

It is a political and social disunion that extends to every city and state. Few Americans have friends on both sides of this continental divide. Gone are the days when some friends voted for Ike, some for Adlai, and nobody considered the others to be traitors or bigots. Today, it’s far more likely that your colleagues at work and your friends at Starbucks share your views, read the same websites, and watch the same cable news. They don’t just agree with you. They think the other side is clueless—and evil. Those voting for the other team are up to something terrible. They can’t possibly be sincere, much less patriotic.

They may be up to something terrible, but they are sincere, and they definitely believe they have the country’s best interests at heart. That’s why the division is so profound and so difficult to bridge. They are certain they gave the cashier a $20—and, dammit, the cashier must know that. The only explanation is that he’s trying to cheat me.

We saw that during the 2016 campaign. Trump’s partisans, in their “Make America Great Again” hats, didn’t just think Hillary was a political adversary. They thought she ran a criminal enterprise, funded by people who wanted an inside track and would pay her and Bill big money to get it. Her crimes would never be prosecuted because she was being protected by a corrupt federal government.

Their chant, “Lock her up,” was disturbing because, for the first time since Watergate, it framed American politics in overtly criminal terms. But it is crucial to understand that the outrage of these chanting partisans was genuine. And they were not inventing their charges out of whole cloth.

Today, Democrats are equally genuine in believing that the Trump campaign may have cooperated with the Russians to steal the election, or at least tilt it unfairly. If true, that’s not just criminal. It would be a treasonous attack on the foundations of American democracy. The current crisis is severe because each side is making very serious charges, each has some suggestive (but not conclusive) evidence, and each is utterly sincere—the rarest of political sentiments.

If both sides trusted the government’s standard procedures to investigate and prosecute crimes, these disputes could be sorted out in the normal way. Alas, nobody does. Republicans considered Attorneys General Eric Holder and Loretta Lynch little more than Democratic Party lapdogs trained to ignore misconduct by Obama’s White House and Hillary Clinton’s campaign. Democrats managed to get the current AG, Jeff Sessions, to recuse himself from the department’s biggest case. Everything James Comey said in 2016 and 2017, when he headed the FBI, was refracted through a partisan lens. As a consequence, the reputations of Congress, the FBI, and the Department of Justice lie in ruins.

How serious do professionals think the crisis is? The best indicator is the unprecedented scale of leaking, especially of highly secret information. My conclusion: Many professionals in the intelligence community and the Justice Department—and perhaps some inside the Trump administration itself—believe that this president is doing things that endanger the country. They are not leaking for the usual reason—to favor their policy. They are leaking as a patriotic duty.

On the other side, Trump’s people think a “deep state” is pushing back, trying to destroy an outsider who came to Washington to change things. What they see is an unconstitutional effort to drive a duly-elected president out of office. These entrenched interests are essentially committed to pulling off a coup d’état.

In this dark tangle, there are two bright spots. One is the bipartisan collaboration between Sens. Richard Burr (R-N.C.) and Mark Warner (D-Va.), who are leading the Senate investigation into Russian interference. If they can ultimately produce a report signed by both sides, they will go a long way to restoring confidence in government.

The other is Robert Mueller’s appointment as a special counsel for the Justice Department. The former head of the FBI is an experienced, non-partisan investigator. Although his record handling high-profile investigations is hardly flawless, his integrity is unquestioned by either side. However, as many observed, there are cautionary examples indicating how easy it is for special prosecutors to overreach. The investigations last too long, go off on tangents, or reach for an easy trophy to display.

Mueller knows those dangers and, hopefully, can avoid them. He is not only a true, independent professional, he’s the only person with the stature to actually clear the president and his closest aides if they are innocent. It is crucial he move quickly, despite the complexity of the case, because the charges themselves are paralyzing Washington.

Until we get some results, remember the wise advice of England’s wartime poster: keep calm and carry on. And remember, too, that the other side’s worries are just as real and troubling as your own.