Americans are heading to the polls for midterm elections which will decide who controls the upper house of Congress – the Senate – with opinion polls showing the Republicans as the favourites to win.
They already control the House of Representatives and need six seats to control the Senate for the first time since 2006.
If they manage to gain a majority in both chambers it would mark the most dramatic political shift since President Obama first entered the White House.
The elections are being seen as a litmus test of his performance in office. His low public approval rating of 40 percent made him a liability on the campaign trail in some states. He may face pressure to make policy changes if his party loses the Senate.
Republicans are running a tight race to retain their seats in Georgia and Kansas. Mitch McConnel of Kentucky has been polling slightly ahead of his Democratic contender and has his eye on becoming Senate majority leader.
Democratic senators are battling it out in the swing states of Colorado and Iowa. Midterms usually punish the party in power, and could be a indicator for the presidential race in 2016.