The race for the White House entered a new, decisive phase yesterday as Barack Obama introduced Senator Joe Biden of Delaware, a seasoned Washington veteran, as his running mate, describing him as ready to “step in and be president”.

In the same historic setting at the Old State Capitol in Springfield, Illinois, where he put on the mantle of President Abraham Lincoln to launch his campaign last year, Obama described Biden as a “statesman with sound judgment who doesn’t have to hide behind bluster to keep America strong”.

In a declaration of war, Republicans swiftly moved to kick Biden by pointing to his criticisms of Obama, their disagreements over the Iraq war and his reputation for verbosity.

From now on, the rival camps will be battling hammer and tongs and the campaign can only get nastier.

The selection of Biden, 65, showed that Obama, who is seeking to become America’s first black president, is mindful of the charge that voters have yet to entrust him with the stewardship of the nation and job of commander-in-chief.

As chairman of the Senate foreign relations committee, Biden has the experience to play the role of wise counsellor to Obama, 47, and the ability to take the fight to John McCain, the Republican nominee, over the war in Iraq and the battle against terrorism.

In front of a huge, sweltering crowd, Obama presented Biden, 65, as a scrappy “working-class kid” who is as at home in a bar as on Capitol Hill, telling the story of his stutter as a boy, the tragedy of losing his wife and young daughter in a car crash and his familiarity with economic hardship.

He added: “That’s the kind of fighter I want on my side.” The crowd cheered and waved newly minted Obama-Biden placards.

The news of Obama’s choice as vice-presidential running mate began unconventionally with a text message to supporters in the early hours of yesterday on the eve of the Democratic national convention in Denver, Colorado.

Biden showed yesterday he was ready to engage in a bare-knuckle contest with McCain, his friend, for offering four more years of President George W Bush’s policies and took a swing at him for being wealthy and out of touch.

He described Obama as a “clear-eyed pragmatist” with “steel in his spine” and said he had earned his respect on the campaign trail.

With Obama and McCain neck and neck in the polls, the election is likely to get personal. Republican activists are already mooting “Obama Bin Biden” bumper stickers.

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