Nixon's major crime was loyalty to his friends.
As a result, he helped to cover up an investigation into wrongdoing.
He was threatened with impeachment by the large-majority Democrats after much hounding by the Old Media. Representatives of his party, Republicans, took a walk from the Capitol to the WH to ask in a private conversation that he resign. Nixon further showed his loyalty to his friends and his country by doing resigning, instead of forcing the party and country to split in a trial over this, though he never believed his actions were wrong. In fact he believed that the state of war gave the executive branch the right to do what his subordinates did, though he never specifically authorized their ill-fated actions, and cited WW2 precedents.
An unbiased history of Watergate would include what I wrote above.
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