Incumbency loses its edge

One major theme to watch for as primary returns start rolling in for Tuesday's key Senate races: Is incumbency all it's cracked up to be?
In most election cycles, holding a seat in Congress is a huge tactical advantage, since sitting lawmakers are usually able to draw on the campaign war chests that national party organizations and congressional campaign groups build up — in addition, of course, to all the time that elected officials spend fundraising on their own.

That advantage shrivels, though, when the electorate seems to be in throw-the-rascals-out mode, as seems to be the case so far in 2010. Rather than coasting into a lavishly funded media push in the homestretch of their primary races, two veteran senators — Arlen Specter of Pennsylvania and Blanche Lincoln of Arkansas — are fighting for their political lives. In Kentucky, the battle for the seat opened by Republican Jim Bunning's retirement is between a candidate endorsed by the state's GOP hierarchy, led by Senate Minority Leader Mitch McConnell, and the self-described tea party candidate, Rand Paul. Tuesday's ballot may well signal the depth of popular anger at Washington — and might serve as a bellwether for which party ultimately gains control of Congress in November.

Pennsylvania
When Arlen Specter switched parties a year ago, he made no secret of his main motive: political survival. Facing a nasty GOP primary against onetime opponent Pat Toomey, Specter wasn't sure he could win. In any other case, such candor might help a candidate, but not this year. Even though Specter often siphoned off some Democratic support in his previous Republican campaigns, the longtime senator has struggled to convince members of the Democratic base that's he really one of them. In recent weeks, Joe Sestak, a Democratic congressman from the Philadelphia suburbs, has closed the gap with Specter, earning endorsements from groups like the abortion-rights group NARAL and MoveOn.org. And Sestak has been savvy not merely in questioning Specter's party loyalty, but also in joining the chorus of other primary challengers denouncing incumbent politicians and campaigning for a "new generation" in Washington. To counter that argument, Specter has been highlighting his "experience" in his own campaign messages. That's not just a dig at Sestak's limited time in Congress, but also a reminder of Specter's long resume in the Senate. Unfortunately for Specter, that may not be much of a selling point for voters Tuesday.

Holly Bailey is a senior political writer for Yahoo! News.