A mid-April CBS/New York Times poll put Congress' approval rating at 13 percent, with 77 percent disapproving of how members are handling their jobs. Another poll, conducted by Quinnipiac in mid-April, had approval for Democrat and Republican members of Congress at 27 percent and 23 percent respectively.

Historically, voters have valued experience. Half of the Senate's current members first served in the House, including seven of the 16 who were newly elected in 2010.

But over the past three election cycles -- two strong Democratic years before the Republican wave of 2010 -- voters have been looking more and more for candidates viewed as fresh faces. The biggest examples two years ago were Mike Lee's upset of 18-year Senate veteran Robert Bennett in Utah's GOP caucus and veteran GOP Rep. Mike Castle's loss in Delaware's GOP Senate primary to tea party-endorsed Christine O'Donnell.

"Republican primaries, especially on the Republican side, reward those who go to the extremes as opposed to rewarding those who seek to govern and lead," said Democratic consultant Chris Lehane.