The assumption has always been that Congress does less during election years, primarily for two reasons:
A) that they're spending their time campaigning at home, rather than legislating in Washington; B) that they're hesitant to take any political stances that could be used against them in an election year fight.
Congress keeps detailed records its time in session via the Résumé of Congressional Activity, and there are, in fact, measurable and significant differences in the amount of time Congress spends in session in election vs. non-election years. In off-years when there is no election (last year being the most recent example), the Senate spends an average of 165 days in session, compared to 156 days for the House.
But in congressional election years, like this one, that number falls to 159 for the Senate and 139 for the House. And during presidential election years like 2012, the drop is even steeper: 142 days in session for the Senate and 129 for the House.
So does it follow from this that Congress is actually getting less work done? Not exactly. Congressmen do tend to introduce fewer bills during election years — the volume of bills introduced drops by nearly 50 percent in both House and Senate for election vs. non-election years. But believe it or not, the volume of bills passed during election years nearly doubles, in both House and Senate.
More interestingly, this isn't a statistical fluke — in every single two-year congressional term since 1947, more bills have been passed in the second year of the term than in the first. This is readily apparent when you look at the trend lines below — the jagged peaks and valleys mark the alternation between off- and election years.
Partially, this reflects the structure of the two-year congressional term: Congressmen introduce bills during the first year of the term, which always falls on an off-year, and then pass those bills — or at least a very small portion of them — during the second year.
Moreover, "bills passed" is a blunt instrument for measuring congressional productivity. It doesn't distinguish between, say, a bill to rename a post office and the Affordable Care Act. It is also important to note that the overall trend of bills passed is down sharply from 50 years ago, while time in session has held generally constant.
But this should dispel the notion that Congress sits on its hands during election years. If anything, the compressed schedule, with fewer days in session combined with the looming deadline of the end of term and uncertainty thereafter, seem to spur Congress to action.