Victory speeches: Bob McDonnell, Chris Christie and Michael Bloomberg
Republicans have scored victories in two key US elections for governor, one year after Barack Obama was voted in as president.
In Virginia, Republican candidate Bob McDonnell won by a comfortable margin, while another, Chris Christie, ousted the Democrat governor in New Jersey.
In New York, independent Mayor Michael Bloomberg narrowly won a third term over Democrat challenger Bill Thompson.
But Democrats won a traditionally Republican House seat in New York.
Correspondents say the gubernatorial defeats are a setback for Mr Obama, who had campaigned in both states for his party's candidates, as he tries to reform healthcare, pass a climate change bill and rally support for his handling of the war in Afghanistan.
Jonathan Beale, BBC News, Washington
In reality the Virginia and New Jersey polls were not simply a referendum on Mr Obama.
Exit polls in both states showed a small majority still approved of how he is running the country.
It is the economy that seems to have been the main concern - that and a host of parochial and even personality issues.
All in all it looked like a good night for Republicans - except there was a sting in the tail.
It came in upstate New York's 23rd congressional district, which has been in Republican hands for more than a century.
Last night it voted Democrat thanks largely to a bitter row within Republican ranks.
It was hardly a good night for President Obama. But it could have been much worse.
While local issues have been paramount in these races, Republicans said the momentum was now behind them ahead of next year's crucial mid-term elections.
Meanwhile in Maine, voters in a referendum rejected a same-sex marriage law passed by state lawmakers earlier this year.
The law was put on hold when conservatives launched a petition to repeal it.
In New Jersey, the incumbent Democratic Governor Jon Corzine had fought a bitter campaign against his Republican rival Chris Christie, not only attacking him over his ties to former President George W Bush and his views on abortion and healthcare, but also poking fun at his weight.
Mr Christie was ahead with about 50% of the vote when Mr Corzine conceded.
Mr Obama had thrown his weight behind Governor Corzine, repeatedly travelling to New Jersey to back the former Goldman Sachs chief executive on the campaign trail.
But Democrats played down Tuesday's gubernatorial defeats.
Obama is in that tricky post-euphoria, pre-delivery phase - it's even trickier if people feel deliverance never comes
"These races turned on local and state issues... and despite what some will certainly claim, the results are not predictive of the future or reflective of the national mood," said Democratic Party chairman Tim Kaine.
However, the Republicans said it was a "warning shot" to the White House.
"[Voters] are tired of the spending, tired of the waste and tired of the over-reach they see coming out of Washington," said House deputy Republican leader Eric Cantor.
In Virginia, Democratic party candidate Creigh Deeds lost in a landslide to his Republican rival, former attorney general Bob McDonnell.
Only last year President Obama became the first Democratic candidate to carry the state since 1964, although its last two governors have been Democrats.
But independent voters who supported the president in the 2008 election seem to have switched their support to the Republican party candidate in this race.
In other results:
Democrat Bill Owens won the House of Representatives seat for New York state's 23rd congressional district, defeating Conservative Party candidate Doug Hoffman
California Lt Gov John Garamendi won a special election to a Northern California congressional seat, keeping the district in Democratic hands
In New York city, independent Mayor Michael Bloomberg won a closer-than-expected race for a third term. With nearly all votes in, he had beaten Democrat Bill Thompson by 51% to 46%
In Atlanta, councillor Mary Norwood could become the city's first white mayor in a generation if she wins a December run-off against Georgia Senator Kasim Reed, after neither received more than half the votes cast
Mayoral elections were also held in Houston, Boston, Detroit and Pittsburgh.
Tuesday's results are being pored over for clues as to how the two main parties will fare in the 2010 mid-terms.
The entire House of Representatives, about a third of the Senate and two-thirds of governors faces the vote next year.
US MEDIA REACTION TO THE RESULTS
Independents have expressed reservations about the president's healthcare efforts and the federal deficit under his leadership. Tuesday's elections provided the first tangible evidence that Republicans can win [independents'] support with the right kind of candidates and the right messages. That is an ominous development for Democrats if it continues unabated into next year.
The Washington Post's Dan Balz says Mr Obama may be losing the vital support of
The Republican victories set the stage for [the party] to raise money, recruit candidates and ride the excitement of an energised base heading into next year's mid-terms. But a Democratic victory in upstate New York - after an ideologically pitched battle between moderates and conservatives over how best to lead Republicans back to power - signalled the Republican Party faces continued upheaval.
Adam Nagourney in the New York Times says
could hamper hopes of an opposition comeback next year.
In the short term, the off-year results will surely colour perceptions within the Washington Beltway, as Obama and the Democratic-run Congress strive to pass landmark healthcare reform legislation, then turn to a major bill to fight global warming. The outcome is unlikely to make things easier for the White House and its allies.
Perhaps most striking were economic views. Voters who expressed the highest levels of economic discontent heavily favoured the Republican candidates in both states - underscoring the challenge Obama and his party may face in 2010 if economic attitudes don't improve.
The votes tonight are anti-incumbent votes in protest at economic crisis and the slow pace of recovery. And they are not, it seems to me, some national referendum on Obama's first nine months. In fact, Obama's approval ratings in both Virginia and New Jersey are respectable and strong, with unemployment headed to 10%.
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