In 1972, Republican Operatives broke into the Democratic Offices at the Watergate. Richard Nixon didn't know about the break in, but he still tried to cover it up. There were payments to witnesses, firing of investigators and officials who were looking into it.
The break in had no effect on the election, the Democrats shit the bed and nominated George "Acid, Amnesty and Abortion" McGovern and Thomas "electric shock" Eagleton and lost 49 states.
But the very fact that Nixon participated in the cover up and obstructed the investigation into it was serious enough to force his resignation.
So now you have the President of the United States openly obstructing an investigation into Russian interference in an American election, going so far to say he believes the Dictator of Russia over our own intel community and law enforcement.