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.
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.
'Warning shot'
But Democrats played down Tuesday's gubernatorial defeats.
"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:
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 independent voters.
"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 Republican infighting 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."
The Los Angeles Times predicts choppy waters ahead for the White House.
"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."
ABC News analyst Gary Langer says it's the economy, stupid.
"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%."
Andrew Sullivan in The Atlantic says it was not a referendum on Obama.
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