When former President of the United States Gerald Ford died in 2007, George McGovern, who was the Democratic nominee in the 1972 election, gave an interview to Larry King where he said this:
MCGOVERN: I have to tell you something I've never said before publicly. I voted for him in 1976.
MCGOVERN: When he -- yes, I did. And at Thanksgiving dinner that year, I never said anything about this to Eleanor or to her five children. But I told them at Thanksgiving time I had voted for President Ford, even though he lost. And I told them why, because I thought he had come in at a difficult time. I didn't know President Carter very well then. And I just felt more comfortable somehow with Gerry Ford. Whereupon my wife Eleanor said, so did I vote for him.
We went around that table -- this is hard to believe -- all five of my kids voted for him. So they get seven votes out of the McGovern family for President Ford and Senator Dole, my long-time Republican friend.
I voted for Carter again in 1980. So with my brand of political luck, I voted against Carter when he won, I voted for him when he lost. But I can justify both of those votes.
This is remarkable, considering that in 1972 George McGovern ran against Richard Nixon, whom Gerald Ford had served under as Vice President. (Though as @jwodder pointed out, it was Spiro T. Agnew, not Ford, who was Nixon's running mate in the 1972 election; Ford replaced Agnew as Vice President a year after Nixon was re-elected.)
But my question is, what were George McGovern's public pronouncements at the time? Did he publicly support Jimmy Carter in the 1976 election, and then just vote for Ford in the voting booth? Or did he just remain silent?
By the way, I got this tidbit from this Op-Ed by conservative writer Jim Geraghty.
EDIT: This bit of information from the 1972 Democratic Primary might explain McGovern's reticence to support Carter in 1976:
Georgia Governor Jimmy Carter helped to spearhead a "Stop McGovern" campaign.