What gave the tape such force, however, was that, by the time everyone heard it, the public knew Nixon was heading a vast cover-up. So far, at least, the Russia investigation looks unlikely to yield this sort of irrefutable evidence.

Establishing obstruction of justice can be complicated. You have to find that someone acted “corruptly,” with intent to impede something like an investigation or court case. This is hard to do — unless you know what kind of misdeed the person is trying to cover up in the first place.

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So what sort of misdeeds could Trump be covering up? We don’t know. But there’s no evidence yet that he’s engaged in — or even has the imagination to engage in — anything more exotic than garden-variety commercial corruption.

Shakespearean tragedy this is not.

In contrast, many details of the Watergate break-in were clear almost immediately. The burglars were arrested in flagrante delicto. Within hours, D.C. cops and the FBI had discovered the group’s ties to the White House and Nixon’s re-election campaign, and began following the money trail. Were higher-ups involved? Judge John J. Sirica got the answer by threatening the burglars with decades-long prison sentences.

We still don’t know everything, of course. We don’t really know whether Nixon ordered the break-in. No living person probably knows what the burglars were actually looking for. It may be that no dead person knew for sure, either. (Charles Colson, widely considered Nixon’s consigliere, once told The New York Times that the burglars were working for Howard Hughes. Don’t think about that too much.)

The scandal’s juicy parts — Deep Throat, Senate hearings, Saturday night massacre, 18-1/2-minute gap — were all about whether Nixon was involved in the cover-up. At the end, thanks to the tapes, we got the answer. But we still don’t know why Nixon went to such self-lacerating lengths to cover up the break-in.

Let’s leave aside the secondary scandals — like shady campaign contributions — that sprouted like mushrooms from the Watergate muck, and stick to the basics. Nixon had a keen (critics said paranoid) sense of domestic threats, from major anti-war demonstrations to the leaking of the Pentagon Papers in June 1971. That’s when Nixon talked to Colson and White House Chief of Staff H.R. Haldeman about burglarizing — or even firebombing — the Brookings Institution, where one copy of the Pentagon Papers was stored. The next month, the White House Plumbers were born.

The reason the Watergate cover-up followed the break-in so seamlessly was that Nixon himself was involved in some of these previous events.

And the cover-up almost succeeded.