The political firestorm over the billions of dollars in earmark requests that led to the scrapping of the $1.1 trillion omnibus spending measure offers a window into a debate that's likely to dominate any number of hotly contested races in 2012.

Charges over earmarks are already flying in a handful of would-be 2012 Senate contests, even among those who have yet to officially declare their rumored candidacies.

Rep. Denny Rehberg (R-Mont.), a potential challenger to Sen. Jon TesterJonathan (Jon) TesterFive things to know about Sanders’s single-payer plan Where Dems stand on Sanders's single-payer bill Overnight Regulation: DeVos ignites backlash with rewrite of campus sexual assault policy l EPA power plant rule decision likely this fall | Panel approves Trump financial regulator nominees MORE (D-Mont.) in 2012, has been trading attacks with the Democratic senator over earmarks for the better part of the past two weeks.

Although Rehberg told The Hill that he hasn't made any decisions on 2012, he recently slammed Tester and Sen. Max BaucusMax Sieben BaucusBernie Sanders flexes power on single-payer ObamaCare architect supports single-payer system Trump has yet to travel west as president MORE (D-Mont.) in a statement after both voted against a ban on earmarks in the Senate. Rehberg is one of many House Republicans who have sworn off the practice amid rumblings that they're gunning for higher office in 2012.

"People in my state are saying, 'enough is enough,' " Rehberg said. "They want us to get a handle on this wasteful spending."

After coming under fire for his earmark vote, Tester penned an open letter to Montana voters explaining his support for the earmarking process, telling voters he has "the authority and the responsibility to make sure our rural state has the resources we need through these appropriations."

The Democrat then fired a return salvo at Rehberg, asking him to make public all of the earmark requests he has put forth during his tenure in the House, which happens to be a pretty long list.

It's one of many burgeoning 2012 Senate races that will likely pit a Republican trying to purge their earmark past against a Democrat trying to balance a tough posture on spending and deficits with their own defense of the practice.

"He conveniently changed his position on earmarks when he got to Congress," Rehberg said of Tester. The Republican points to an '06 Senate debate, during which he claims Tester pronounced his blanket opposition to the practice. "He said he was against earmarks, period. There's not much wiggle room in that stance."

A spokesman for Tester said Rehberg and other critics of the Democratic senator have repeatedly taken his words out of context, emphasizing that Tester's issue was with the transparency of the earmarking process. On his Senate website, the Democrat lists every earmark he's requested over the course of his first term.

As for Rehberg, his name was attached to some $100 million in earmarks for FY 2010, according to the website, which tracks earmark requests. It's a figure Rehberg says is wildly inflated thanks to requests from Montana's two Democratic senators.

"Actually, I didn't [request much] in relation to everyone else," Rehberg said. "I'm getting credit for what Sen. Baucus and Sen. Tester got in the Senate."

The Republican hasn't requested a single earmark for FY 2011 and said he has no intention of requesting any in the future.

A similar spat erupted in Nebraska Thursday after Republican state Attorney General Jon Bruning used Sen. Ben Nelson's (D-Neb.) opposition to the earmark ban in an e-mail fundraising appeal. Bruning is the lone Republican already declared against Nelson for 2012.

Nelson, who has defended the process as necessary to secure funding for vital projects in his home state, quickly hit back at Bruning, claiming that one of the earmarks he secured in 2009 came at the Republican's request. Bruning's response: He never wanted the money and the state intends to send the money back.

In Nevada, rumored 2012 Senate contender Rep. Dean HellerDean Arthur HellerSenate Dems hold floor talk-a-thon against latest ObamaCare repeal bill Lawmakers grapple with warrantless wiretapping program Overnight Health Care: New GOP ObamaCare repeal bill gains momentum MORE (R-Nev.) was the only member of the state's congressional delegation who didn't have millions in earmark requests included in the recently-shelved omnibus measure. Heller, too, has sworn off the practice, requesting not a single earmark for FY 2011, despite requesting some $22.5 million in earmarks during FY 2010.

Heller could end up in a primary with Sen. John Ensign (R-Nev.), who has yet to announce his 2012 intentions, but backed the Senate earmark ban and came out against the omnibus, even though it had some $100 million of his own earmark requests contained in it.

Outgoing Sen. George LeMieux (R-Fla.) is one potential 2012 hopeful who has managed to stay completely clear of earmarks during his short appointed tenure in the Senate. The Republican, who may challenge Sen. Bill NelsonClarence (Bill) William NelsonDem asks airlines to cap airfares ahead of Hurricane Maria Trump encourages Rick Scott to run for Senate Overnight Regulation: House moves to block methane rule | Senators wrestle with allowing driverless trucks | EPA delays toxic waste rule MORE (D-Fla.), hasn't requested a single one.

Rep. Connie Mack (R-Fla.), another potential Nelson challenger in 2012 has also sworn off the practice, requesting nothing for FY 2011 after requesting some $10 million in earmarks during FY 2010.

Nelson recently voted in favor of the Senate earmark ban, despite defending the practice just two weeks earlier. Republicans in the state have already pounced on the flip and Nelson's prolific earmark past.

The Democrat, who will be a top GOP target in 2012 if he chooses to seek reelection, was one of only two Senate Democrats who voted for the ban. The other — Sen. Claire McCaskillClaire Conner McCaskillGOP sees fresh opening with Dems’ single payer embrace Senators blast internet subsidy program It is time to make domestic terrorism a federal crime MORE (Mo.) — is also near the top of the GOP target list in 2012.