Obama UN
Barack Obama's Democrats could lose out as the Republicans may recapture control of the US Senate Reuters

Republicans could be in the enviable position of recapturing control of the US Senate, with the likelihood of making major gains, in midterm elections on Tuesday 4 November in polls that could be mirrored as a public referendum on Barack Obama's performance as president.

Millions of Americans will take to the polls to cast votes and elect 36 senators, 36 governors and all 435 members of the House of Representatives in campaigns influenced by Obama's low job approval rating, partisan gridlock in Washington and a US economy not growing widely enough to help many in the middle class.

However, despite the possibility that the Republicans are likely to increase the number of seats it holds in the US Senate, polls have revealed eight to 10 races could go either way. It is unclear whether the party will be able to win the six seats that are required to control the 100-member chamber for the first time since the 2006 election.

The race for control could extend to later in the year or even the start of 2015. Senate races with multiple candidates in Louisiana and Georgia, where the winner must get more than 50% of the vote, could be forced into runoffs in December and January, respectively.

Republican control will damage Democrats

The Republicans will get complete control of both chambers of Congress if they win the battle for the Senate.

If this likely outcome does become a reality, not only will Obama have to deal with the most dramatic political shift since he entered the White House, his final two years will be complicated, with compromises high on the agenda when dealing with his Republican opponents.

Speculation is rife that Mitt Romney could run for the US presidency in 2016 Reuters

The White House has tried to dismiss Obama having to make strategy changes, with spokesman Josh Earnest noting many of the contested Senate races where Democrats were in trouble were in states the president lost to Republican Mitt Romney in the 2012 election.

"It would not be wise to draw as broad a conclusion about the outcome of this election as you would about a national presidential election simply by virtue of the map," he said, as reported by Reuters.

Democratic senators are battling for re-election in tough races in Alaska, Arkansas, Louisiana and North Carolina, all won by Romney in 2012. Mark Udall is in a tight race in Colorado while the fight to replace retiring Tom Harkin in Iowa could go either way

All change in the Senate seating plan

Republicans have a challenge to retain their seats in Georgia, where Senator Saxby Chambliss is retiring, and Kansas, where Republican Senator Pat Roberts is being challenged by an independent.

Republican Senate Leader Mitch McConnell of Kentucky, has an edge over Democratic challenger Alison Lundergan Grimes according to polls, would take the place of Democrat Harry Reid as Senate majority leader if the Republicans win the Senate and he hangs on for re-election.

We're talking about votes in a bunch of states that didn't vote for the president
- White House official

"Obviously, we intend to be a responsible governing Republican majority, if the American people give us the chance to do that," McConnell told ABC News, as reported by Reuters.

Obama's low public approval rating of around 40% made him a political liability in some states on the campaign trail, where his last campaign appearance was on Sunday 2 November in Philadelphia.

If the Democrats do lose the Senate, the president will be under pressure to make changes at the White House. According to a poll by Reuters/Ipsos, 75% of respondents believe Obama's party needs to "rethink" how major issues facing America are approached. Meanwhile, 64% said Obama should replace some of his senior staff after the election.

However, it is unlikely there will be any sort of Obama administration shakeup, according to a White House official. They told Reuters: "We're talking about votes in a bunch of states that didn't vote for the president."