If it is wrong for Republicans to fuel their campaigns with corporate cash, then it is wrong for Democrats to do so.

That was the no-hold-barred message that Russ Feingold brought to Netroots Nation.

“Sometimes we have to be very direct with the Democratic Party itself,” the former senator from Wisconsin told the thousands of bloggers, thinkers and activists who packed the great hall at the Minneapolis Convention Center. “I fear the Democratic Party is in danger of losing its identity.”

Feingold was talking about the decision by some Democrats that the party must form so-called “super-PACS”—political action committees that use corporate money in much the same way that Republicans have.

If Democrats fuel their campaigns with corporate cash, the senator said, “we’ll lose our souls.”

“I don’t just think it’s wrong. I think it’s a dumb strategy,” he continued, to the enthusiastic crowd hushed and listening to a speech that went far beyond the standard rhetoric of this pre-presidential election year. “Democrats should never be in the business of taking unlimited corporate money…. It’s dancing with the devil…. [The voters] will see us as corporate-lite.”

Anyone who thought they were going to hear a feel-good speech from Russ Feingold got a surprise.

The former senator from Wisconsin, long a favorite of the progressive blogosphere, did not come to suggest that all the world’s problems were caused by awful Republicans or that all the solutions would come from Democrats.

The fiercely independent Democrat, who cast the sole vote against Patriot Act and took the lead in opposing the wars in Iraq and Afghanistan, may have made a name fro himself fighting the worst excesses of the Bush administration. But he was never a yes-man for the Obama administration. Feingold cast a relatively lonely vote against making Tim Geithner the secretary of the Treasury, and an even more lonely vote against banking reforms that failed to address the threat posed by “too-big-to-fail” banks. And he fought Bill Clinton, George Bush and Barack Obama on trade policy.

Feingold’s speech was framed around the Citizens United ruling by the US Supreme Court, which struck down legislative barriers to corporate spending on campaigns. He decried the court’s 5-4 ruling as he has since it was issued last year a "lawless decision” that “overturned more than one hundred years of statutes and case law” designed to keep special-interest money out of politics.

His deeper message, however, was a call to action for progressives to practice a politics of principle rather than simple partisanship—a theme that is central to the work of the national reform group he leads, Progressive United. Yes, he argued, Barack Obama should be reelected in 2012. Yes, he hopes that Democrats make a comeback after the devastating 2010 election cycle that cost him his Senate seat and cost his party control of the US House and governorships across the country.

But, he warned, a victory-at-any-cost approach will cost the party the credibility it needs to attract Americans who are disgusted by political corruption—and yield little in the way of progress.

Decrying the failures of the Obama administration on issues ranging from bank regulation to tax policy to trade agreements, he urged progressives—especially progressive bloggers, who have become such a powerful influence in the party—“to call out Republicans and Democrats” who fail to stand for reform.

Feingold’s was not an Obama trashing speech, however. It was an Obama prodding speech.

He urged bloggers to cheer the president on if Obama issues an executive order requiring government contractors to reveal their campaign contributions—a move the White House is considering.

And the former senator—who many in the crowd urged to seek an open Wisconsin Senate seat in 2012 or challenge Wisconsin Governor Scott Walker in a recall election—did not stop there.

He urged the president to make reforming a corrupt system central to his re-election campaign messaging.

Fighting the abuses made possible by the Citizens United ruling, and taking the steps necessary to overturn it, should be a pivotal plank of the president’s 2012 campaign, Feingold said.

“It should be in every speech, every statement,” Feingold said of the reform message.

“We can overturn Citizens United,” Feingold said, recalling that a single appointment to the Supreme Court could tip the balance against the corporate interests. “But to get there, the influence of corporate interests in these campaigns has to be front and center.”

And the netroots crowd can put in there, the former senator said.

“Together, we can call out the Democratic Party when it strays from its ideals,” Feingold declared. “And, together, we can take our country back.”