As well as sending a warning sign to Republicans across the country, the outcome of the governor's race in Virginia has focused fresh attention on the outgoing Democratic governor, Mark Warner, already being tipped as a candidate for the presidency in 2008.
In the battle for the White House this time last year, President Bush secured Virginia by a 10-point margin. Twelve months later, Mr Bush made an 11th-hour intervention on behalf of the Republican candidate, Jerry Kilgore, only to see Mr Kaine win by 52 points to 46. Two per cent of the electors voted for an independent candidate.
"This has been a long and difficult campaign. We've done it. We've done it," Mr Kaine told his ebullient supporters in the state capital, Richmond, on Tuesday evening.
"Tonight, the people of Virginia have sent a message - that they like the path that we chose and they want to keep the state moving forward."
In a similar battle in New Jersey a Democrat, Jon Corzine, won a nasty and hard-fought contest for the state's governorship, securing the contest by a surprising nine-point margin. While New Jersey has traditionally been a Democratic state, Virginia has not.
With the congressional elections still a year away, the orthodox opinion is that the local elections held in so-called "off" years have little value as harbingers to the future. But this year - certainly in the case of Virginia - Mr Bush gave the contest a broader context by placing himself into the equation.
"It's certainly a bloody nose for Mr Bush," said Stephen Hess, a former speechwriter for President John F Kennedy and a professor of media and public affairs at George Washington University. "He did not have to campaign at the very last minute for Kilgore. It's as if he feels this is more significant."
Mr Bush and his administration were already on the back foot after months of low ratings as a result of the continuing chaos and violence in Iraq, rising petrol prices and the fallout over the indictment of the Vice-President's chief of staff, Lewis Libby.
An opinion poll published on Tuesday by the Pew Research Centre put Mr Bush's rating at just 36 points - the lowest of his presidency.
The realisation that Mr Bush's personal input was not enough to turn around the situation in Virginia will be of considerable concern to Republican candidates who are already concerned about going to the polls next year carrying the baggage of the prolonged war in Iraq.
A House representative, Rahm Emmanuel, chairman of the Democratic Congressional Campaign Committee, said: "Our voters, going into the mid-term elections are mobilised and energised. Theirs are despondent."
The result in Virginia has also drawn fresh attention to the political future of the outgoing Democratic Governor, Mark Warner. Mr Hess said that Mr Warner was able to use his personal popularity and appeal to ensure a victory for Mr Kaine, his lieutenant-governor. In effect, Mr Warner's coat-tails were longer than Mr Bush's.
For the Democratic Party, which needs to find a candidate with national appeal for the 2008 presidential election, the youthful Mr Warner, 50, a moderate, southern Democrat, could yet prove to be an attractive option. The last three Democratic presidents - Bill Clinton, Jimmy Carter and Lyndon Johnson - have all come from the South.
"I think to a large extent [the story] is the Warner influence," Mark Rozell, a professor at George Mason University, told The Washington Post.
"He created the circumstances for a Democrat to win in a Republican-leaning state in the South."
Results from other local elections look to have fewer national implications. In New York, the incumbent Republican, Michael Bloomberg, was always expected to win and he did so with a huge margin. His unofficial 20-point win over Fernando Ferrer appears to set a Republican record, beating Rudolph Giuliani's 16-point win in 1997 and even exceeding Fiorello LaGuardia's 19-point landslide in 1937.
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