Pictured: Sen. Tim Johnson of South Dakota may be among the most vulnerable Democratic incumbents facing reelection in 2014, when Republicans will get another shot at taking control of the Senate. (Joshua Roberts, Bloomberg / July 17, 2012)
Republicans are expected to keep their majority in the House, and history would suggest they might expand their numbers in the sixth year of a two-term presidency.
But the Democrats' hold on the Senate is at risk, with competitive 2014 contests for at least nine of their seats -- seven in states Mitt Romney carried in 2012. Republicans would need a net gain of six seats to overturn the Democrats' 55-45 edge.
Voters in those Republican states will be watching as their Democratic senators tackle polarizing issues such as citizenship rights for illegal immigrants, spending levels for social welfare programs and new restrictions on firearms. How the lawmakers line up could well influence their own futures, as well as the fate of President Obama's second-term agenda.
"I am sure that [they] can't wait to have a vote on assault weapons on the Senate floor," Jim Manley, a former aide to Majority Leader Harry Reid, said of Minority Leader Mitch McConnell and the Republican National Committee.
In fact, both parties will be seizing on votes that can become fodder for 30-second attack ads in the races to come. One group trying to block the nomination of former GOP Sen. Chuck Hagel of Nebraska as Obama's Defense secretary is already airing ads in five Republican states where Democratic senators face reelection in 2014.
In an effort to shield fellow Democrats from having to cast politically damaging votes, Reid will employ his power to shape the way legislation is considered on the Senate floor.
"His goal is to look out for the caucus as a whole," Manley said.
How issues like gun control and immigration play out, in broad terms, will frame the contours of the 2014 election.