Centrist Senate Republicans are likely to get a new ally in Sen.-elect Mark Kirk (R-Ill.), according to Sen. Susan Collins (R-Maine).

Collins, one of the most visible centrist Republicans in the Senate, told the Kennebec Journal that the newly elected senator punned to her that he wanted to be a part of the Senate GOP's "Mod Squad." Columnist David B. Offer wrote:

The day after the election, Collins told me she had received a post-election telephone call from Mark Kirk, the Illinois Republican elected to fill the Senate seat once held by President Barack Obama.

“I can’t wait to join your Mod Squad,” Kirk told her. 

The Maine senator's comments highlight the potential tension between centrist and conservative Republican senators in the next Congress.

Tea Party activists, aided by Sen. Jim DeMint (R-S.C.), propelled a number of conservative GOP candidates to victory in Senate primary races across the country. Incoming senators such as Wisconsin's Ron Johnson and Pennsylvania's Pat Toomey made overtures to the activists on the campaign trail.

But Kirk, who positioned himself as a centrist in the House representing part of the Chicago suburbs, was able to buck the trend, handily defeating primary opponent Patrick Hughes.

Centrist and veteran GOP senators were put on the defensive by conservative activists who say they don't stand strong enough on principle. 

Collins has been targeted for straying to the left, even though she does not face reelection until 2014.

Sen. Bob Bennett (R-Utah) was famously defeated by Tea Party-backed candidate Mike Lee in the state's Senate primary, and other establishment candidates such as Florida's Charlie Crist, Nevada's Sue Lowden and Colorado's Jane Norton were pushed out by conservative challengers.

Others such as Sen. Orrin Hatch (R-Utah) are next on the list of GOP senators who could face a primary challenge in 2012. Even Massachusetts Sen. Scott Brown (R), who rode Tea Party support to his surprising January special election win, has angered some conservatives for voting with Democrats on small-business legislation.