Republican Sen. Dick Lugar (R-Ind.), who is already in the sights of Tea Party activists, is the only Senate Republican up for reelection in 2012 to vote against a proposed earmark ban in the Senate Tuesday.

Of the 10 GOP senators whose seats are up two years from now, Lugar is one of several who appears likely to get Tea Party-backed primary challengers. Along with Sens. Olympia Snowe (R-Maine) and Scott Brown (R-Mass.), Lugar stands near the top of the list of centrist GOP primary targets in 2012, but has shown no willingness to shift his positions in an attempt to cater to his party's conservative base. 

Lugar has criticized Senate Republicans for not quickly moving forward on the New START treaty, and earlier this month he declined to sign onto a legal brief challenging the healthcare law.   

The nine other GOP senators up in 2012 all voted in favor of the earmark ban, which fell short of the two-thirds majority it needed for passage Tuesday. The other nine Republicans who voted for it are Sens. Jon Kyl (Ariz.), Snowe, Brown, Roger Wicker (Miss.), John Ensign (Nev.), Bob Corker (Tenn.), Orrin Hatch (Utah), Kay Bailey Hutchison (Texas) and John Barrasso (Wy.). 

Another seven Republicans voted against the ban, but none of them face voters in 2012.

For many Republican candidates this past cycle, earmarks proved a major issue on the campaign trail — a symbol of runaway government spending and Washington excess. It's an issue expected to carry over into 2012.  

Staring down tough reelection races in 2012, Democratic Sens. Claire McCaskill (Mo.) and Bill Nelson (Fla.) were two of just seven Senate Democrats who voted in favor of the earmark ban Tuesday. 

McCaskill, along with Sen. Mark Udall (D-Colo.), was one of the Democratic co-sponsors of the measure, trumpeted by Sen. Tom Coburn (R-Okla.).

The four other Democrats who voted for the measure were Sens. Evan Bayh (Ind.), Russ Feingold (Wis.), Michael Bennet (Colo.) and Mark Warner (Va.). 

Bayh is retiring and Feingold lost to Republican Ron Johnson earlier this month, but both could be candidates in 2012. It's rumored Bayh could make a run for governor and Feingold could try for a return to the Senate, should Sen. Herb Kohl (D-Wis.) decide to retire in two years.

Bennet, who just defeated Republican Ken Buck this fall, isn't up until 2016, while Warner's seat is up in 2014.