Martha Mitchell, John's wife, came in TV when it all started and said her husband was crooked. He dismissed her as nuts. She died from cancer before it was all over and never got to say "see I told you so".
No they fact checked, in fact they had to get two sources for everything.
The problem is that "journalists" wanted to be the next W &B after that and ran with everything.
They weren't famous before the stories came out. In 73-74 I was taking American history in 11th grade and the teacher had us watch the recaps of the daily events on the evening news. She was going over the constitution at the time and was using the current events as a perfect example of it in action.