The nomination of a female running mate had energized the convention, buoying prospects for the underdog presidential candidate, when I ran into a veteran party activist.

“Today, we feel invincible,” she said. “But in a few days, reality will set in.”

The month was July 1984. My friend was a Democratic delegate at the convention that nominated Geraldine Ferraro for vice president. Now, the question is whether Sarah Palin’s infusion of energy to John McCain’s campaign will last longer than the short-lived boost Ferraro gave Walter Mondale’s.

If it does, it would be another remarkable twist in a remarkable election. It has been 48 years since a vice-presidential nominee had a tangible impact on a presidential election outcome.

In 1960, John F. Kennedy’s choice of Lyndon B. Johnson kept Texas Democratic, prompted wary Southern Democrats to back the ticket and united the party for what proved to be a close election.

Palin’s effect is potentially broader but less certain. She remains relatively unknown to many Americans. Polls show most people like her personally but that many are skeptical about her qualifications, attitudes that may vary more than for a better-known figure.

Post-convention polls and growing crowds show the Alaska governor has given McCain a big boost with Republicans, many of whom have been unenthusiastic.

Some polls also show she helped with white women and independents, two crucial voter groups that could be decisive in November. An ABC News-Washington Post poll shows McCain bounced from an eight-point deficit among white women to a 12-point advantage. In several surveys, he took the lead among independents.

The polls also show McCain with one in five voters who backed Hillary Clinton in the Democratic primaries.

If these gains hold, Palin could help McCain win such Republican-leaning states as Missouri and North Carolina and perhaps foil the Barack Obama campaign’s effort to break the recent GOP grip on Colorado, Ohio and Virginia.

Democrats, meanwhile, have been thrown off stride, unsure whether to go after Palin or McCain. Their problems were underscored by a McCain effort to capitalize on Obama’s comment that, even with lipstick, a pig is “still a pig.”

History gives contradictory evidence whether the Palin-fueled bounce will last or recede.

Mondale’s boost after picking Ferraro vanished quickly. So did Al Gore’s post-convention gains.

On the other hand, the 1988 GOP convention propelled George H.W. Bush from behind to a lead he never relinquished, despite negative coverage of his running mate, Dan Quayle.

In each case, voters’ judgments of the top of the ticket proved decisive. Though the focus on Palin may last longer than usual, in part because she delayed the inevitable media interviews, attention inevitably will return to McCain and Obama.

And though the Democratic nominee this week challenged Palin’s positive aura by disputing her positions on budget earmarks and the notorious “bridge to nowhere,” his single best argument is that McCain would continue many Bush administration policies the country opposes.

Besides, despite the hype and favorable publicity for Palin, this week’s polls show the two tickets basically tied. They also show that Obama retains a double-digit lead as the candidate most likely to bring change. And many voters remain concerned about McCain’s age and believe he would maintain Bush policies.

Still, the GOP convention seems to have undone some of Obama’s progress in persuading voters he is ready to be president and a strong leader.

In the end, the debates starting in two weeks are still likely to be decisive. They are Obama’s chance to persuade voters he can do the job, despite a slender resume.

Until then, however, there can be no doubt that Palin’s emergence has added an unpredictable new factor that neither side really expected.