In a primary challenge, of course, a crowded field could benefit Lugar, who would be able to squeak by with a plurality as the other contenders divide up the anti-Lugar vote. (That's what happened in the 2010 Senate primary, helping former Sen. Dan Coats (R) prevail.)
In Maine, a similar situation is emerging for conservatives hungry to take out one of the leading moderates in their party, Snowe. Snowe is one of the least reliable Republican votes, and conservatives in the state are emboldened after electing a Tea Party favorite to the governorship, Paul LePage. A poll, conducted last year by the Democratic firm Public Policy Polling, showed a generic conservative leading Snowe by 28 points.
But Maine doesn't have a plethora of conservative Republicans on the bench; the only candidate to express interest challenging her so far is businessman Scott D'Amboise, a second-tier candidate.
Rhodes Cook, a nonpartisan political analyst, said that the primaries themselves are not be the problem for national Republicans - but, rather, flawed candidates who can't appeal to the broader electorate are. In Kentucky this year, he said, Sen.-elect Rand Paul (R) emerged from a bruising primary and won the general by a healthy margin. Other Republican nominees, like Christine O'Donnell (R) in Delaware, likely cost the GOP seats.
"The lesson from this time seems to be that they are a mixed blessing," Cook said of crowded primaries. "You like their enthusiasm and their votes but sometimes Republican leaders can be bitten by their choice in candidates. So it depends on the pedigree of the challengers."
Republicans are also flooding races where the GOP could pick up seats. In Montana, several Republicans are already moving forward with campaigns to take on Democratic Sen. Jon Tester, a prime pick up opportunity for Republicans. Bozeman businessman Steve Daines is expected to announce this week that he'll challenge Tester, while Rep. Denny Rehberg (R) and D.C. based terrorism expert Neil Livingstone (R) is also reportedly considering the race.
Rehberg, who has elected in 2000, would be considered the front runner -- and establishment favorite -- in the race.
The GOP may also face problems in defending other seats besides Lugar's. In Nevada, scandal-plagued Sen. John Ensign (R) has made no indication that he won't seek re-election and would be very vulnerable in the general election. Nevada political guru Jon Ralston wrote Wednesday that if Ensign does run he would be "flattened" by Republican Rep. Dean Heller, should he decide to run.
"I have to believe Ensign will soon become a target of the National Republican Senatorial Committee," Ralston wrote. "Why? Because the GOP sees a path to taking the Senate in 2012 -- two-thirds of the contested seats are held by Democrats -- and they don't want to have to worry about defending their own. Ensign has a disapproval rating approaching Harry Reid-like elevation and he will have neither the benefit of a Reid-like turnout machine or campaign team."
Another name that has been floated in Nevada: 2010 contender Sharron Angle, who knows a thing or two about winning crowded primaries.
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