"What did the President know, and when did he know it?"
"What did the President (Nixon) know, and when did he know it?"
That famous question asked by Republican Howard Baker is often held up as a beacon of principle, with a Republican willing to seek out the tough answers in Watergate.
Sorry to be the bearer of cynicism, but Baker's famous question was part of a partisan strategy to protect Nixon. The question was a red herring. All the Republicans in congress recognized that Nixon had covered stuff up, but they were confident that Watergate break-in and other Plumber felonies had been rogue operations that Nixon had no prior knowledge of.
And there could never be any hard evidence of Nixon ordering a cover-up, right? One guy's word against another. Hey, Nixon can survive this. Paint Dean as a sour-grapes liar. Hammer away that Nixon had no prior knowledge of the crimes.
The long-shot strategy was to compartmentalize the president. Re-frame the scandal in terms of the president's personal involvement. Since a dozen close Nixon advisers were going to end up in jail they needed a trial of the man, not of his administration.
D'oh! They didn't know about the tapes, and they didn't know Nixon.
It became an accidental profile in courage when it turned out that Nixon was on tape free-associating about various felonies he could authorize, and knew a hell of a lot, and a lot earlier, than Howard Baker could imagine.
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The preceding account/analysis came to me via that multi-part PBS series on Watergate a few years back.