That was in the 68 campaign (i.e. I'm a bit young to remember much of it personally, unlike Watergate and the fall of Saigon). How much effect it really had can be argued. One thing I do know is that even later the Paris talks weren't looking all that promising until at least 1972, and Thieu had to be strongarmed to go along. Whether Johnson/Humphrey could have delivered Thieu to the negotiating table even without interference is a question we'll never know the answer to.
There's plenty of things to dislike about Nixon. He's always been a mixed bag in a lot of ways. Yes, he was a crook. But, some of the diplomacy during his administration may have reduced the chance for nuclear war (dÃ©tente with the USSR, and the opening with China).
In some ways, his Vietnam policy is similar to Obama's in Iraq. Then it was called Vietnamization, now it's called having the Iraqi's assume responsibility for their security. In the case of Nixon, we have 40 years of history to know it didn't work very well. In 40 years, we'll know a lot more about how Iraq works out.