Colin Powell, the Republican once tipped to become America’s first black President, endorsed the Democrat, Barack Obama, yesterday as a “transformational figure” who was ready to be the next Commander-in-Chief.

President Bush’s former Secretary of State said that he was backing Mr Obama, not because of his race, but because he had met the standard to be an exceptional President. And he delivered a stinging rebuff to the Republican, John McCain, describing his campaign as petty and troubling.

Endorsements rarely have a decisive impact in presidential politics, but the effusive backing for Mr Obama by a man so widely respected could play a significant role in persuading some undecided voters. It also ensures that the news will dominate media coverage of the campaign for the next 24 hours, robbing Mr McCain of one more day to change the trajectory of the race with only two weeks to go until the election on November 4.

At a rally in North Carolina, Mr Obama basked in the endorsement, calling General Powell “a great soldier, a great statesman and a great American”. He added that he was beyond honoured and deeply humbled to have his support.

General Powell, who oversaw victory in the 1991 Gulf War, made clear that his decision to back Mr Obama was as much a sign of his unhappiness with Mr McCain, his campaign and his choice of Sarah Palin to be his running mate. General Powell, an avowed moderate, said that Mr McCain’s choices in recent weeks — especially his selection of the Alaska governor — had raised questions in his mind about the Arizona senator’s judgment.

“I don’t believe she’s ready to be President of the United States, which is the job of the Vice-President,” General Powell said bluntly. He decried what he called the “rightward shift” of the Republican Party — he cited Mrs Palin’s selection as an example — and criticised Mr McCain’s “unsure” response to the economic crisis. “Almost every day he had a different approach to the problems we were having,” General Powell told NBC’s Meet the Press.

Mr McCain, who has known General Powell for 25 years, sought to play down the endorsement, saying: “It doesn’t come as a surprise.” He pointed out that he had been endorsed by four other former Republican Secretaries of State.

General Powell, 71, who was also the National Security Adviser to Ronald Reagan, said that he had asked himself: “Which is the President we need now?” Referring to Mr Obama, he continued: “And I come to the conclusion that because of his ability to inspire, because of the inclusive nature of his campaign, because he is reaching out all across America, because of who he is and his rhetorical abilities — and you have to take that into account — as well as his substance — he has both style and substance, he has met the standard of being a successful President, being an exceptional President.

“I think he is a transformational figure. He is a new generation coming . . . on to the world stage and on the American stage. And for that reason I’ll be voting for Senator Barack Obama.”

General Powell criticised Mr McCain for invoking the Vietnam-era domestic terrorist William Ayers as an Obama associate. “I think this goes too far. And I think it has made the McCain campaign look a little narrow. It’s not what the American people are looking for. And I look at these kinds of approaches to the campaign, and they trouble me,” he said.

“I feel strongly about this particular point,” he added. “We have got to stop polarising ourselves in this way.”

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