With the 113th Congress sworn in, it's worth remembering that relatively few members of the House got here in a tough election fight, as is typical for the House. The overwhelming number won their seats comfortably last November. Two-thirds of House members won their elections by 20 points or better, or had no major-party opponent at all.
This is partly because partisanship isn't just relegated to Congress - 94 percent of partisan voters nationwide voted for their party's House candidate, so districts with a majority of Republicans vote for Republicans, and districts with mostly Democrats generally send Democrats to D.C. This pattern overshadows the fact that Americans tend to disapprove of Congress as a whole.
Only 27 House members in the new class won by under five percentage points, including just 12 Republicans and 15 Democrats who did - hardly the kind of breakdown that has a lot of members of either side looking over their shoulder, or feeling the need to show crossover appeal back home.
Given that, we can start to profile the districts with the closest balance of Democratic and Republican voters. (It's too early, of course, to tell which will really emerge as hot races, since there are so many factors, but if we see members from some of these districts charting a centrist course over the next two years, this could be part of the reason.)
To make a partisan index for each congressional district, we looked at both the district's votes for major state and Presidential contests over the last two cycles, applied to the newly-drawn districts. The average partisan vote from state contests was weighted more heavily than the Presidential vote, to help account for the sometimes-large differences between national candidate performance and state- and local- candidate performance. Historically, the latter tend to be a slightly better predictor of Congressional voting, particularly in the South and Midwest.
The most evenly balanced districts we label "marginal" and you'll see these mostly have partisan indexes or around 2 or less; many even zero. On average, partisan races in these districts are decided within a few points. Once we see indexes north of 3 points or so, that's a "lean" district where one party has an edge in partisan voting.
There are a couple of districts here worth noting where a member continues to hold a seat despite the district's partisanship leaning the other way; these kinds of members often have strong personal appeal that transcends partisanship and may well continue to, but their districts' balance often has them tacking toward the center, so they're worth including here.
This hardly means other districts are out of the spotlight, though - "safe" districts are always potential places we could see action in the primaries. Many members have to consider the possibility of drawing a primary challenge more so than having to face the overall electorate. And not just a primary defeat; a serious challenge, even if pushed back, drains money and resources and can push a member further to an ideological side which leads to a harder general election fight.
Of course, we make a mistake if we think that ideological stances, compromise or voting on spotlighted national issues is only about the voters "back home" in the district; local constituencies aren't the only things members have to consider nowadays. They have to make the national party and national-level donors happy too. That factor, plus the rise of super PACs, could easily put members in the crosshairs of groups with larger agendas than just within their own congressional district, or gin up a primary challenge.
*The same-party contests this year, an artifact of redistricting, are counted here as landslide wins for the party.
CBS News consultant Mark Gersh contributed to this report.