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Minutes after an aide to John McCain effectively described Sarah Palin as unhinged — the latest sign of open war inside the embattled Republican campaign — the two candidates were roared on to a stage yesterday in Pennsylvania, a state that is central to their ever narrowing path to victory.

Mr McCain lavished praise on his running-mate, who was standing a few feet away next to a group of women waving “Pitbulls for Sarah” signs, before declaring: “By the way, when two mavericks join up we don’t agree on everything, but it’s a lot of fun.”

As Mr McCain made his last stand in Pennsylvania, where he is banking on a surprise victory to rob Barack Obama of the presidency now within the Democrat’s grasp, fresh reports of infighting made it clear that things are far from fun in the Republican camp.

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In the past week, aides to the Arizona senator have briefed reporters anonymously against Mrs Palin, describing the Alaska Governor as a “diva”. Yesterday a far harsher pejorative emerged: one called her a “whack job”, a term usually reserved for people who are dangerously unbalanced. Yet if there were tensions between the candidates they put on a rousing display of unity, with Mr McCain delivering perhaps his most impassioned and effective speech of the campaign.

Pennsylvania is the only state that voted Democrat in 2004 that he is trying to peel away from Mr Obama. In Hershey — home to the chocolate empire — Mr McCain spoke to a passionate crowd of 5,000. “It’s wonderful to be back in Pennsylvania and it’s wonderful to fool the pundits, because we’re going to win Pennsylvania!” he declared, to thousands of waving American flags. Despite trailing his rival in the Keystone State, and in national polls, Mr McCain’s aides insist that there is still a path to victory next Tuesday, albeit one that allows little room for error. Central to the plan is winning Pennsylvania and its 21 electoral college votes.

First, they argue, he must defend enough “toss-up” states won by President Bush — especially Florida, Ohio, Missouri, Indiana, North Carolina and Virginia — where they say Mr Obama is not assured of victory. Aides to the Democrat acknowledge that Ohio and Florida are still very close.

If Mr McCain can hang on to nearly all those states, he then hopes to offset likely defeats in Colorado, New Mexico and Nevada with a win in Pennsylvania, where Mr Obama also campaigned yesterday. The Democrat travelled to the state where he was crushed by Hillary Clinton in the primaries — and the subject of his controversial remark about working-class people “clinging” to guns and religion — after pleas from Ed Rendell, the Democratic Governor, to return. Mr Rendell said that he was getting “a little nervous” about the state.

Mr McCain lambasted Mr Obama for his comment to the voter known as “Joe the Plumber” that he wants to “spread the wealth around” and accused him of a policy of defeat in Iraq.

Using the word “fight” nine times in his speech, Mr McCain declared: “Stand up, stand up, stand up and fight! Let’s go win this election!” It was a powerful performance. Mr McCain hopes that it has not come too late.

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