Though endorsements tend to reinforce voter predispositions rather than change them, polls have suggested a nod from Powell might make a difference among some voters. Powell's endorsement may be unusual in that it both crosses the partisan aisle and comes from a particularly well-liked quasi-political figure -- one, as a bonus, who's steeped in the military experience Obama lacks.
Perhaps heightening that effect, Powell gave a scathing critique of the McCain campaign as he endorsed Obama, saying he was "disappointed" by the approach the Republican side has taken on the issues.
"I have some concerns about the direction that the party has taken in recent years," Powell said. "It has moved more to the right than I would like to see it. But that's a choice the party makes."
Powell also expressed concern with the selection of Alaska Gov. Sarah Palin as McCain's vice presidential nominee.
"She's a very distinguished woman and she's to be admired," Powell said, "but at the same time, now that we have had a chance to watch her for some seven weeks, I don't believe she's ready to be president of the United States, which is the job of the vice president. And so that raised some question in my mind as to the judgment that Sen. McCain made."
Powell, who served as President Bush's secretary of state during his first term, becoming the first African American to reach that office, voiced concern over McCain and Republican National Committee campaign tactics.
He cited the GOP's effort to tie Obama to former 1970s radical William Ayers.
"This Bill Ayers situation that's been going on for weeks: Why do we keep talking about him. Why do we have these robocalls [arguing about an Obama-Ayers link] going around the country?" Powell asked.
Troubled by conservative whispers that Obama is a Muslim, Powell gave a passionate defense of Obama and Muslim Americans.
"The correct answer. He is not a Muslim," Powell said. "He's a Christian. He's always been a Christian. But the really right answer is: 'What if he is?' Is there something wrong with being a Muslim in this country? The answer is no. That's not America."
He cited a story about a Muslim American solider who died serving in Iraq to argue that Muslim Americans also love and defend America.
Powell cited the economy as the most important issue the next president will have to deal with, and said that he's convinced Obama would better lead the country out of the economic crisis.
"In the case of Mr. McCain, I found that he was a little unsure as to how to deal with the economic problems we're having," he said.
Powell's comments were part of a big day for Obama, whose campaign announced that it raised an astounding $150 million in September -- easily an all-time record. The haul continues a huge money advantage Obama has built over McCain since forgoing public financing for his campaign.
But the McCain campaign got in a few shots today, as well, responding to Obama's Fayetteville comments on the Powell endorsement with a slap at the Democrat.
"Only an unproven and inexperienced politician like Barack Obama would have to rely so heavily on an another man's resume in making the case for his own candidacy -- and it shows that he's just not ready," said Tucker Bounds, a spokesman for McCain-Palin 2008.