Q&A: US mid-term elections 2010
The US has been holding mid-term elections, which decide the balance of power in Congress over the next two years. The Republicans made sweeping gains as they won control of the House of Representatives, but the Democrats retained a slim majority in the Senate.
What do the results mean for President Barack Obama?
President Obama's name did not appear on any ballot paper, but the elections are widely seen as an appraisal of his performance over the last two years.
Going into the mid-terms, his Democratic Party had a majority in both houses. Having lost control of the House, the president will now have to work closely with Republicans as he tries to push through legislation.
Former presidents have mostly been able to develop a working relationship with congressional leaders of an opposing party.
However, things do not always go smoothly. A Republican-controlled Congress effectively shut down non-essential government services for short periods in 1995 and 1996 because President Bill Clinton refused to make certain budget cuts.
How big are Republican gains?
Prior to the elections, the Democrats controlled 59 seats in the Senate (including two seats held by independents who caucus with the Democrats) and had a majority of 39 seats in the House.
Counts have not yet been completed, but projections suggest the Republicans have obtained a net gain of at least 60 seats in the House.
It would mark the biggest exchange of seats in the House since 1948, when the Democrats gained 75 seats. It also surpasses the swing in 1994, when the Democrats lost 54 House seats.
In the Senate contest, the Republicans made gains but fell short of gaining the 10 seats needed to win control.
Even so, it will be harder for the Democrats to muster the 60 Senate votes they need to stop Republican delaying tactics.
The Republicans also gained at least 10 of the 37 governorships in contention.
What was behind the Democrat losses?
The state of the economy was the top election issue. It is thought to have been very damaging for the Democrats - unemployment stands above 9%.
The result is also seen as a sign of frustration with President Obama, who was elected in 2008 on a platform of hope and change.
Republican John Boehner, who is set to take over as House speaker, said the vote was a repudiation of Washington and "big government".
The rise of the anti-establishment Tea Party movement, which campaigned against what it sees as an excessive growth of government, boosted the Republicans.
What will happen to President Obama's agenda?
It is up to the powerful majority leaders in both houses to set the legislative agenda. Committee chairmen are also chosen from the ranks of the majority party.
The current Congress will now return for a "lame-duck" session before newly-elected members take their seats in January.
One of the issues to be discussed is the extension of tax breaks introduced by George Bush, with Republicans calling on President Obama to extend them for the rich as well as the middle class.
Next year, Mr Obama will try co-ordinate with the Republican-led Congress, though he could also use his executive power more assertively if the Republicans try to block the Democratic agenda.
The president recently listed three of the areas where he might be able to work with a new Congress: reducing public spending, and immigration and education reform.
Other issues, including environmental reform, are likely to be put on hold.
What about legislation that's already been passed?
President Obama may have to fight off attempts to repeal his healthcare reform.
Republicans have promised to try to unravel the reform either by repealing sections of it or retracting financing from key provisions. They could even try to replace the reform with their own bill, but President Obama can veto this.
The Republicans have also said they want to roll back financial regulation introduced by Mr Obama in the wake of the global financial crisis.
Who was being elected?
The elections are called mid-terms because they come half-way through the four-year term served by the president, though the polls are in fact for Congress - the two houses of the US legislature - and for some state governorships (gubernatorial elections).
In Congress, all 435 members of the House of Representatives faced the voters, as they do every two years. But only about a third of the 100 seats in the Senate are up for grabs at any one time. This year, 37 Senate seats were being contested and there were 37 gubernatorial elections.
Does the president's party normally do badly in mid-terms?
The party of a sitting president often loses some seats in mid-term elections, particularly in a president's first term.
Since 1946, the average loss in a president's first term is 25 seats in the House of Representatives and three seats in the Senate. Truman (in 1946) and Clinton (in 1994) both lost 54 House seats, while Johnson (in 1966) lost 48.
Why not elect everybody at the same time?
The American system is designed to be overlapping, both in terms of the powers of the different bodies and in terms of when people are elected to them.
The House of Representatives is the larger of the two houses of Congress. It was set up as a popular body, with the number of members tied to the size of the population. The idea was for it to directly and quickly reflect the public mood, which is why the members face election every two years.
The Senate was planned as a more reflective body - senators serve for six years. Each state has two senators regardless of its size.