Your challenge, should you choose to accept it, is to have Spiro Agnew elected President by 1976, with a POD after 1969. Nixon may be assassinated, but only after the '72 election.
John Erlichman said:"I'm sort of afraid to have him [Agnew] go too [on a trip to Asia]," Nixon said deadpan, repeating his joke about the assassin's dilema. "If they kill Nixon, they get Agnew. I'd hate to have anything happen to him."
John Erlichman said:I concluded that the man [Agnew] was exceedingly narrow; new thoughts were uncwelcome to him.
John Erlichman said:Nixon found early that personal meetings with Agnew were invariably unpleasant. The President came out of them amazed at Agnew's constant self-aggrandizement.
John Erlichman said:...in late July 1971, the President interrupted our daily meeting to tell me his latest Agnew problems. The President had recently announced that he would be making his historic trip to China. Now Agnew, in Africa on a tour, had told the leader of one nation that he disagreed with the President's China policy. Agnew said he didn't think the forthcoming trip was a good idea. The President was very agitated. "It is beyond my understanding," he said. "Twice Agnew has proposed that he go to China! Now he tells world its a bad idea for me to go! What am I going to do with him?"
Well it would be rather simple to just not have him either accept the bribes or have the bribes not come to light until later.
In October [1973], he was formally charged with having accepted bribes totaling more than $100,000, while holding office as Baltimore County Executive, Governor of Maryland, and Vice President of the United States.
IMO, Nixon should've dumped Agnew in 1972 and replaced him with Reagan. Agnew has a Bidenesque mouth and a Palinesque intellect if Ehrlichman is to be believed.