US President George W Bush's first Secretary of State, Colin Powell, has endorsed Democratic election candidate Barack Obama for the White House.
Backing Mr Obama over John McCain, the Republican Party's choice to succeed Mr Bush in November, he said the Democrat had the "ability to inspire".
"All Americans... not just African-Americans" would be proud of an Obama win, he argued.
Mr McCain said he was not surprised at his "long-time friend's" decision.
He pointed out that other former secretaries of state had backed his own candidacy, naming them as Henry Kissinger, James Baker, Lawrence Eagleburger and Alexander Haig - all Republicans.
Meanwhile, the Obama campaign announced it had raised a record monthly total of more than $150m (£86m) in September.
The total figure of $605m dwarfs the total of Mr McCain, who chose to stay within the public campaign financing system.
Mr Powell's endorsement carries weight, says the BBC's Rachel Harvey in Washington.
It [an Obama victory] would not just electrify our country, it would electrify the world
former US secretary of state
This is in part because, as a former chairman of the Joint chiefs of Staff and former secretary of state, Colin Powell's backing says to undecided American voters "I trust this man as the Commander in Chief and so you should too", our correspondent adds.
Mr Powell's support will be seen as a significant boost to the Obama campaign a little over two weeks before voting day.
This is not a decision Colin Powell has taken lightly, our correspondent says.
He has spoken to both Mr McCain and Mr Obama regularly and watched carefully and he has concluded, he says, that Barack Obama has the style and substance to lead America in the future.
But it is perhaps the sharp criticism of the recent conduct of John McCain's campaign, for being too negative and too narrow, that will do most damage to the Republican candidate, our correspondent adds.
That approach, Mr Powell said, is not what the American people are looking for.
"I think he [Barack Obama] would be a transformational president," Mr Powell told NBC's Meet The Press.
An Obama victory would should "not just electrify our country, it would electrify the world", he said.
Mr Obama was better suited to handle America's economy, the former secretary of state said.
"In the case of Mr McCain... you got the sense that he didn't have a complete grasp of the economic problems that we had," he argued.
Mr Powell was also "concerned" at the selection of Governor Sarah Palin" for running mate believing her not ready for the White House.
And President Bush's first secretary of state criticised his own party for allowing the campaign to turn negative.
"I'm also troubled by, not what Senator McCain says, but what members of the [Republican] Party say... such things as 'Well, you know that Mr Obama is a Muslim'.
"Well the correct answer is, 'He's not a Muslim, 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."
"It isn't easy for me to disappoint Sen McCain in the way that I have this morning, and I regret that," Mr Powell added.
Mr McCain was campaigning in Virginia this weekend
Speaking on Fox News, Mr McCain said he had "always admired and respected Gen Powell".
"We're long-time friends," he said. "This doesn't come as a surprise."
Mr McCain criticised Mr Obama for opting out of public financing for his campaign.
"History shows us where unlimited amounts of money are in political campaigns, it leads to scandal," he added.
Mr Obama was heading for North Carolina on Sunday after drawing big crowds in traditionally Republican Missouri. Mr McCain has been campaigning in Virginia.