"The likelihood was that (McCain) was going to lose anyway," said Zelizer, adding that Palin "went out on the field and played poorly. But that's not a game-changer. She just continued the trend in the game."
Gone are the days when regionalism or the "favorite son" factor may even make a difference, as Texas Sen. Lyndon B. Johnson did for John F. Kennedy in the South in 1960. The electorate has grown far too polarized, Zelizer said, and most voters already know whether they're choosing the Republican or the Democrat, regardless of the No. 2.
For example, picking Sen. Rob Portman of Ohio, once considered a front-runner in the Romney running-mate contest, would have provided no guarantee that Romney would win Ohio.
In Ryan's case, the same goes for Wisconsin, Zelizer said. Wisconsin Republicans have displayed their strength this year, beating back an effort to recall Gov. Scott Walker. But at the same time Democrats still angry over that outcome could react strongly to the Ryan VP pick and work that much harder to get out the vote for Obama.
"Ryan can lose Wisconsin as much as he can win Wisconsin for Romney," Zelizer said. "So, again, it will come down to the Romney-Obama debates and their campaigns, rather than Ryan himself."
Joel Goldstein of Saint Louis University, a vice presidential scholar, agreed that the running-mate choice itself doesn't typically tilt the scales. However, there is one possible exception to that rule: "For it to make a difference you have to start with a close election," he said.
Isn't that just what we have this year?
"I don't think what Romney does is going to swing 10 percent of the vote or anything. I think you're talking about a few percent," he said. "That may not sound like very much, but on the other hand, in a close election, that can be the whole difference."
Walter Mondale may have been that difference in 1976, when he and Jimmy Carter narrowly defeated Gerald Ford and Bob Dole, Goldstein said. He noted that Mondale campaigned hard in states such as Ohio, Pennsylvania and Wisconsin, where the vice presidential candidate was popular, and the Democratic ticket won.
And, certainly, the choice does make a difference in other ways. Palin drew so much attention from the media and a public just getting to know her that the spotlight often shone brighter on her than on McCain and his message. The same could happen with Ryan, another relative unknown to most Americans, said Goldstein.
The pick can also offer clues as to what the presidential nominee perceives his weaknesses to be. In this case, was Romney worried about turning out a GOP base that has shown indifference toward him and thus chose Ryan, the primary author of a conservative budget plan that excites tea party Republicans? Perhaps, said Goldstein. Or maybe he's hoping Ryan's budgetary expertise will help steer the conversation away from Romney's own personal finances — and personal style — and back to the campaign's central issue: the economy.
After 2008, McCain advisers acknowledged that one goal of the Palin pick was to cut into Obama's lead among women voters. That didn't happen.
Nevertheless, in several studies of the "Palin effect," researchers found that her impact was more substantial than other vice presidential picks of the past. She excited the Republican base and rallied Democratic partisans. Her initial rise, then fall, in favorability ratings tracked closely with McCain's poll numbers.
But did she cost him the election? Researchers say no. One study, by analysts at Stanford and Duke, found that Palin may have cost McCain about 1.6 percent of the vote, hardly enough to change the outcome.
Still, the Palin legacy and the impact of a VP choice this time were very much on the minds of GOP faithful here in a state especially stung by McCain's loss in '08. They not only expressed some relief in the selection of Ryan; some firmly believed Romney's choice for VP would make a big difference.