AS IF Barack Obama did not have enough trouble dealing with a Republican-controlled House of Representatives, his party could lose the Senate, too, at elections in November. That would make his last two years in the White House very different from the early parts of his presidency. Assuming that the Republicans hold the House, which is likely, they would control both arms of Congress. Mr Obama would have to work with them or risk irrelevance. How likely is this to happen? Republicans need a net gain of six seats, which is a lot, but the winds are blowing in their favour. Some of the reasons relate to the national mood: the economic recovery has been disappointing and many Americans are fed up. Mr Obama is not on the ballot, but his reputation matters. His woeful management of the rollout of his health reform has dented the Democrats' reputation for competence, such as it was. His low approval rating (43% by the RealClearPolitics poll of polls) will weigh his party down.

Other reasons are to do with electoral mechanics. There are 100 senators—two from each state, regardless of population. They serve six-year terms. Every two years, a third of seats come up for re-election. The election of 2008 was a huge triumph for Democrats (it was the year Mr Obama first won the presidency), so they prevailed in several states where they normally lose. That means that this year they are defending plenty of seats they will find hard to defend. Four Democrats are struggling to survive in states Mitt Romney won in 2012: Mark Begich in Alaska, Mark Pryor in Arkansas, Mary Landrieu in Louisiana and Kay Hagan in North Carolina.

In addition, five Democratic senators are retiring or have quit, including three in states Mr Obama lost by more than ten percentage points in 2012 (South Dakota, West Virginia and Montana). Only three Republicans are retiring, and all are from states that their party can lose only if it does something truly moronic. That is not impossible: Republican primary voters sometimes select candidates for ideology rather than electability. Indeed, six sitting Republican senators are facing challenges from the right. But attentive crystal ballgazers think this will be a good year for the Grand Old Party, and a big headache for the man in the White House.

Dig deeper:

The "party of no" is offering some fresh ideas (February 2014)

Barack Obama's state-of-the-union address revealed a leader waiting for something to turn up (February 2014)

Essay: Democracy has run into trouble. What can be done to revive it? (March 2014)