Robert Reich, who served as Secretary of Labor under former US President Bill Clinton, tells the BBC the present Congressional Republican leadership has "not been in the practice of coming up with legislation" and has focused instead on frustrating the president's agenda.

Jim Gilmore, the Republican former governor of Virginia, tells the BBC he is very confident his party will prevail in the Senate.

"The burden is on us now to offer a positive agenda."

Republicans have retained Senate seats in Tennessee, Mississippi, Maine and Oklahoma, exit polls find.

Barbara Plett Usher
BBC state department correspondent

tweets, external: Tough climate for #Democrats party official tells #BBCMidterms, but stresses all incumbents still in play #Midterms2014

In West Virginia - a state where coal is central to the economy - 53% of voters think climate change is not a serious problem, according to a preliminary ABC exit poll.

Image source, Getty Images

Franz Strasser
BBC News, Minnesota

Robert from St. Paul, Minnesota, says Republicans taking control of the Senate can make a difference.

"You will have the attempt to enact the agenda of skewing in the direction of wealthy people."

Judd Gregg, former Republican Senator and Governor for New Hampshire, told BBC World Service if Republicans win Congress tonight they can no longer be a "party in the negative", they must show the American people they are willing to govern.

Karen Tumulty, Washington Post correspondent

tweets, external: Shelley Moore Capito is the first Republican that WV [West Virginia] has elected to the Senate since 1956.

Image source, Reuters

A supporter of US Senate Minority Leader Mitch McConnell raised this sign at his election rally in Louisville, Kentucky

Republican Shelley Moore Capito is the projected winner of a West Virginia Senate seat formerly held by a Democrat, the first GOP Senate gain of the evening.

If Democrat Mike Michaud wins the governor race in Maine, he will become the first openly gay governor in the US.

Image source, AP

Russell Lewis, National Public Radio

tweets, external: North Carolina State Board of Elections is holding an emergency meeting now - to decide extending poll closures in 3 counties.

Most mid-term voters reported being pessimistic, and they were more than twice as likely to say that life will be worse for the next generation than to say things will get better, according to an Associated Press exit poll.

Barbara Plett Usher
BBC state department correspondent

tweets, external: Local official tells #BBCMidterms of long voter lines in #NorthCarolina, expects polls to stay open beyond closing time #Midterms2014

Colorado is often described as the bellwether state. It has swung Obama's way in recent years amid political and demographic change, but some experts believe it could hold the key to a Republican win if they can snatch it. The BBC's Anthony Zurcher paid the state a visit.

Newsday, BBC World Service

Sam Ibrahim, the Republican County Chair for New Hanover in North Carolina, tells us that polls will stay open after 8pm Eastern time due to high turnout.

Most of the attention on mid-term election day is focused on the voters, but far more Americans will not be going to the polls. Survey data has found that the demographics of non-voters are quite different than likely voters.

Reid Wilson, Washington Post

tweets, external: Tim Scott is the first elected African American senator from South Carolina.

The Republican party also held two seats in South Carolina as Senators Tim Scott and Lindsey Graham won their elections.

Paul Kane, Washington Post congressional reporter

tweets, external: Here at McConnell campaign HQ, the call was so quick that most people don't even seem to realize that their candidate has won.