The ad is a major departure from McCain's previous commercials, which have relentlessly attacked Obama's character, with the most recent tying him to 1960s Chicago radical William Ayers, a member of the Weathermen, as part of an effort to push the idea that he is "too risky for America".
The spot, called 'Fight', has McCain sat in a chair speaking for the entire ad direct to camera. It opens with McCain saying: "The last eight years haven't worked very well have they? I'll make the next four better."
In a break with previous ads, the spot fails to mention Obama once, while the tone is softer and more relaxed, in contrast to the aggressive attack ads the Republicans have been using.
The move comes after Republican campaign strategists realised McCain's ads were failing to resonate with voters, who were turned off by references to Obama's past, and more concerned with contemporary worries such as the economy.
The ad is being rolled out as the liberal-leaning US broadsheet The Washington Post throws its weight behind Obama.
The paper, which endorsed Democrats in the last two presidential elections, endorsed Obama in an editorial saying the Illinois senator "has the potential to become a great president".
The newspaper said its choice was influenced by the negative campaign of McCain and his decision to pick the highly inexperienced and untried Sarah Palin, the governor of Alaska, as his vice-presidential running mate for the November 4 election.
"It is made easy in larger part, though, because of our admiration for Mr Obama and the impressive qualities he has shown during this long race," the Post said.
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