New York: Republican Bob Turner wins 'Obama referendum'
President Barack Obama has been dealt a double setback after Republican wins in two seats, including one billed as a referendum on his economic policies.
In New York, Republican Bob Turner won a key election to succeed Democratic Congressman Anthony Weiner, who quit in June over a sex texting scandal.
The retired media executive is the first Republican to take office in New York's ninth district since the 1920s.
Meanwhile, Mark Amodei defeated Democrat Kate Marshall in Nevada.
Addressing jubilant supporters after his win, Mr Turner said people had voted against the president's "irresponsible" fiscal policy.
Backed by former New York City mayor Rudolph Giuliani, Mr Turner said the vote was a "referendum" on President Obama.
Correspondents say losing the election will be a symbolic blow to the White House at a moment when President Obama is beginning his bid for re-election amid low approval ratings.
Anthony Weiner, who served in the House for seven terms, resigned in June after it emerged he had sent a series of images to a number of different women via Twitter.
With 84% of votes counted, Mr Turner had won 54% of votes compared to Democratic state assemblyman David Weprin's 46%, the Associated Press reported.
Mr Turner said the result sent a "loud and clear" message to Washington.
"We've been told this is a referendum. Mr President, we are on the wrong track. We have had it with an irresponsible fiscal policy which endangers the entire economy," Mr Turner told supporters.
The ninth district, encompassing parts of southern Brooklyn and south-central Queens, has long been a traditional Democratic stronghold.
Registered Republican voters are outnumbered in the traditionally blue-collar, Catholic and Orthodox Jewish district by a margin of three to one.
A key plank of Mr Turner's campaign was aimed at the district's Jewish community, appealing to their support of Israel and painting Mr Turner as the only candidate guaranteed to stand up for the interests of the Jewish state.
During the campaign, Republicans made Mr Obama the focus of at least as many attacks as David Weprin, a member of the New York state assembly and the actual Democratic candidate.
In response, the Democratic Congressional Campaign Committee reportedly spent more than $500,000 (£320,000) on TV advertisements.
Former President Bill Clinton and New York Governor Andrew Cuomo recorded phone messages for registered Democrats in an effort to win over undecided voters.
Meanwhile in Nevada, Republican Mark Amodei won the election to fill a vacant seat in the House of Representatives.
Mr Amodei beat Democrat Kate Marshall in the rural northern Nevada district that has never elected a Democrat.
The previous post-holder, Republican Dean Heller, was appointed from the House to the Senate in May to replace Republican John Ensign, who resigned over a sex scandal.