Question

What series of events brought down the Nixon presidency?

Answer 1

The Watergate Scandal

Ultimately, Richard Nixon resigned the presidency to avoid impeachment for his role in covering up the Watergate break-ins.  The Pentagon Papers were related to this, because the "Plumbers" group that perpetrated the Watergate break-ins were formed because of leaks of confidential information like the Pentagon Papers.  And the Saturday night massacre was related also, because that refers to Nixon's firing of the special counsel who was investigating Watergate and the subsequent resignations of the Attorney General and the Deputy Attorney General.  But it was the Watergate Scandal itself that was at the center of Nixon's downfall.