1-Johnson considered flying to the Chicago convention and re-entering the race for the nomination. The Secret Service couldn't guarantee his safety so he thought better of it.
2-He had direct evidence of Nixon sabotaging the Paris peace talks over Vietnam. He didn't use it himself because it would have meant revealing FBI and NSA bugging operations.
3-He did pass some of the intelligence to Hubert Humphrey but this was just before the election and Humphrey thought he would win so he held off because it would be too disruptive to the country.
Now 1 maybe just changes the outcome of the 1968 election but it strikes me that 2 or 3 could have been more damaging than Watergate. That after all was strictly domestic politics; stretching out the Vietnam war would have cost American lives.
Anybody want to give their take on the consequences?