Sorry, this part:
Plus how a McGovern presidency would go.
Who would be a better replacement for Eagleton - Gaylord Nelson? A lot of people said no to McGovern.

Although maybe a different campaign beforehand would make them more kindly to him - definitely want to avoid the whole "Abortion, Acid" comments.
Hmm... Heck I'll give it a try. McGovern pretty much wins the nomination as he did OTL. After that, somehow, make it so that he isn't giving his acceptance speech at 2 am (I think that was the time he gave it) and instead somehow have him give it the next day, so more people can watch. Also, have him do more to reach out to the old new dealers in the party, so that it's more unified going into the general election. Then, with a better vetting process, have him pick a different running mate (I don't have any names at the top of my head, maybe Carter or Dale Bumpers to balance the ticket regionally and ideologically). You also need the Democrats to keep both the far left/hippies and the Dixiecrats quiet. Then, have Watergate break out in say, August perhaps and have it drag on, with Nixon trying to cover it up and shooting himself in the foot in the process. Then, as an October surprise, have Agnew's tax evasion come out. With all of that baggage , and with the fringe of the party on both ends (far lefties and Dixiecrats) kept in check, McGovern wins by a hair.
As for his Presidency, you might get Healthcare reform and troops are pulled out of Vietnam. Outside of that, it sucks. The economy is still going to go south and there will still be an energy shortage in 1973, Saigon will still fall and I can see the Democratic party dividing itself the way it did in the late '60s. The 1974 midterms go strongly for the GOP but not enough to flip either chamber of congress, especially the house. With all of that, Ronald Reagan wins in 1976, by a margin similar to Nixon's in '68, deals with the Iranian revolutions (although there may not be a hostage crisis), a second energy crisis, and double digit inflation. He goes on to lose the 1980 election. You'll have 3 Presidencies in 12 years just like OTL.