Russ Feingold could be Wisconsin's next senator. He could also be the highest-profile matryr for the cause of campaign finance reform. It looks increasingly likely that he can't be both.

The Democrat is considering a run to retake the Senate seat he lost to Republican Ron Johnson in 2010. In Feingold's last attempt, he took the extraordinary step of refusing help from party committees and then-new super PACs. The move was in a part a protest of the judicial dismantling of his eponymous 2002 McCain-Feingold Act that was gutted by the Supreme Court's Citizens United decision in 2010, but supporters say Feingold's self-imposed financing limits cost him votes—and possibly a victory—while Johnson benefitted from a barrage of outside help.

Now, as Feingold mulls a second run in the ruins of the system he built, he'll have to decide whether to take 2010's white-glove approach or embrace the reality of a campaign in which the importance of outside groups has mushroomed and their presence is a given in every other Senate battleground.

It's a decision being tracked closely not just by political operatives, but by campaign finance experts in Washington, who say Feingold's career illustrates the massive changes that have swept through the system since Congress approved McCain-Feingold. All of them are curious whether, in their view, he will stick to his principles or yield to political reality.

(RELATED: How Super PACs Will Strengthen Democracy in 2016)

"It's up for conversation what he might think of super PACs that wanted to act on his behalf," said Patrick Guarasci, a Wisconsin-based Democratic operative. "I'm sure he is very aware of the current post-Citizens United landscape that is flush with independent group spending, and I'm sure he would give it very good consideration. As a political operative, I would encourage him to fight with both hands and not one tied behind his back."

Guarasci said Feingold's small-dollar donor base means he could succeed even without super PACs, but many Wisconsin Democrats expect it won't come to that. They point to a February interview by Jon Tester, in which the chairman of the Democratic Senatorial Campaign Committee said his potential recruit understands that "it's a different world now, and he knows that." One Democratic insider in the state, granted anonymity to speak candidly, told National Journal later that month that Feingold knows "he can't fight with one hand tied behind his back."

Feingold, who has no official campaign apparatus, has not publicly indicated what he plans to do. Even those who believe Feingold will accept help don't know how far he would go to encourage it—if, for example, he would raise money for Senate Majority PAC, the main Senate Democratic outside group that can legally host fundraisers with incumbent lawmakers despite rules barring their coordination. Feingold also would have to decide whether to reinstitute his ban on accepting PAC money to his official campaign.

No matter how far he goes to encourage outside group spending, any green light could give Republicans an opening to call him a hypocrite. To them, it would be an important part of a larger argument that Feingold, despite no longer holding office, is the career politician in his race against Johnson.

(RELATED: Secret-Money Group Tied to Marco Rubio Super PAC Has Been Researching Presidential Primary Voters)

"He was a godfather of campaign-finance reform, this was his No. 1 crusade in the Senate, and now he is so desperate to get back to Washington he's willing to throw out all of his previous convictions," said Andrea Bozek, spokeswoman for the National Republican Senatorial Committee. "And that's exactly the type of person he [ran] against when he first ran for Congress two decades ago."

Democrats reject that argument, saying voters won't be swayed by attacks from a party knee-deep in special-influence cash of its own. But a new position from Feingold would be an indication of just how far campaign finance has changed not just since his last campaign, but since 2002, when he successfully shepherded restrictions on how parties raise money. His thought-to-be landmark legislation at the time included a ban on uncapped union and corporate donations to political parties—known as "soft money"—and limits on when groups were allowed to run certain kinds of TV ads.

Most of those restrictions have been striken down by a series of rulings from the Supreme Court, most notably during its Citizens United decision, which have paved the way for super PACs and other so-called "dark money" groups—nonprofits that don't have to reveal their donors—to become massive new players on the political scene.

And to some Republicans, they're gleeful at the prospect of Feingold accepting help from outside groups. To them, Feingold overreached badly in 2002, and they are happy to see him campaign in the ruins of the system he helped build.

"It's kind of refreshing to watching somebody wake up and see the reality they helped make," said one Republican campaign finance expert. "After decrying all these types of practices, to come marching back on the field playing with a corked bat like the rest of them is satisfying."

We want to hear what you think about this article. Submit a letter to the editor or write to