Sank his campaign.  In fairness, Eagleton probably wasn't the all time worst candidate but McGovern should have vetted him better.

This is where it first became obvious that if a candidate for national office had anything in their past to hide, it would be used against them. We have had many vice-presidents less qualified than Tom Eagleton, but to be elected they have to understand that there is no way to hide anything in your past.

Let me reiterate what irishgit has stated in his review: Senator George McGovern could have chosen anyone, maybe even Jesus Christ, for all intents and purposes, and they still would have lost that year. In all fairness, Senator George McGovern and his running mate, Senator Thomas Eagleton proved to be ineffective campaigners facing a presidential juggernaut of domestic and foreign relations successes by Nixon going into 1972. And what eventually proved futile for the Democratic ticket that year was further compounded by the embarrassing revelations of Eagleton's psychiatic treatment- and the desperate move by the Democrats to pick Sargent Shriver as Eagleton's replacement. Richard Nixon and Spiro Agnew in 1972, though laughable today in light of the Watergate Scandal and its legacy, had absolutely no way to lose in 1972. Not even the news of plumbers and breaking into the Watergate complex during that balmy June night of 1972 (granted no one could fathom how big it was going to get) would derail Nixon from his landslide victory later that November. McGovern-Eagleton/Shriver was doomed, and the reality is that the only ticket that could have beaten Nixon that year would have been...Nixon.

Not a bad choice, but really bad background checking. After the nomination it was revealed that Eagleton had undergone psychiatric treatment, and ultimately withdrew from the ticket, being replaced by Shriver.

A lot of people have had psychiatric treatment, but it does carry a stigma, and Eagleton should have known that and revealed it. Ambushing McGovern with the revelation was irresponsible.

Not that it really mattered. McGovern couldn't have beaten Nixon that year if he'd had Jesus Christ on the ticket.