"Postscript: Sargent Shriver" appears on The New Yorker's Web site today.  In it, senior editor Hendrik Hertzberg writes:

In 1972, when George McGovern’s original running mate, Senator Thomas Eagleton, had to withdraw, Shriver defied the family pecking order by taking Eagleton’s place on the ticket. The Democrats had their problems that year, but Shriver wasn’t one of them. He was a magnificent candidate.

It's doubtful that the late Speaker of the House, Tip O'Neill (D-MA), who knew a thing or two about campaigning, would have agreed.