Opponents of big money in politics celebrated some small victories lately: A constitutional amendment to curb campaign spending cleared a key Senate committee and was introduced in the House. And a new “super PAC to end all super PACs” raised $5 million in a matter of weeks.

At first glance, such long-shot causes look inevitably doomed to fail. No one really expects two-thirds of Congress and three-quarters of the states to amend the Constitution in an area as disputed as campaign financing. And numerous super PACs bent on banning unrestricted money have come and gone in recent years, most of them now terminated.

But the latest campaign finance push, however impractical or constitutionally suspect, has tapped a well of voter anger that politicians ignore at their peril. Public disgust with Congress, which according to Gallup now enjoys a record-low 7 percent approval rating, may not impact this fall’s midterm elections. But as erstwhile House Majority Leader Eric Cantor discovered in his stunning loss in Virginia’s GOP primary, voter wrath over big money can exact a political price. Cantor’s primary opponent, tea party Republican Dave Brat, had made the majority leader’s cozy Wall Street and special interest ties a central campaign theme. Brat is now trumpeting the $400,000 he’s raised from small donors as evidence that he’s running a “campaign of the people.”

“People think you can’t win on the basis of this issue, and we want to say, ‘Actually, you can,’ ” said Lawrence Lessig, a Harvard Law School professor who on May 1 founded the Mayday PAC, a crowdfunded super PAC that will back congressional candidates committed to campaign finance changes. “And we want to do it in a way that surprises Washington, inside the Beltway.”

Lessig has already surprised himself and others by pulling in $1 million in the PAC’s first 13 days, then another $5 million by July 4. In an interview with CQ Roll Call, Lessig said he developed his own open source software to raise the money, since the popular Kickstarter crowdfunding tool lacked a platform for political donations. Mayday PAC has now raised $7.7 million of an anticipated $12 million once matching funds from large donors roll in, probably by the end of this month.

If Lessig hits his $12 million target, Mayday PAC will be among the top five highest-grossing super PACs in this midterm. The American Crossroads super PAC organized by GOP operative Karl Rove, for example, raised just $11 million through June 30 of this year, Federal Election Commission records show. Granted, the conservative super PAC’s social welfare affiliate, known as Crossroads GPS, appears to be raising and spending the largest share of the operation’s money in this election.

Still, Lessig’s anticipated $12 million haul is all the more noteworthy given how many super PACs formed with the aim of ending super PACs have fallen flat in recent years. A whole slew of do-gooder super PACs, many of them inspired by comedian Stephen Colbert’s super PAC contests and spoofs, sprung up in 2012. But virtually all of them, from Citizens Against Super PACs to No Dirty Money Elections, raised virtually no money and closed up shop within a year.

An exception is Friends of Democracy, a super PAC headed by David Donnelly, executive director of the Public Campaign Action Fund. That PAC raised and spent about $2.5 million in the 2012 elections, and managed to oust eight of the nine candidates it targeted for defeat. In this cycle, Friends of Democracy had raised $2.5 million through the second quarter, and will announce by the end of this month a new slate of state and federal candidates.

“There’s a tremendous amount of interest in it, and we’re very excited about the work that Mayday PAC and Larry Lessig are doing,” Donnelly said, noting the two PACs do not compete for donors and will coordinate their efforts. “There’s clearly an appetite for expanding this type of work.”

Lessig has generated media buzz and checks thanks in part to his public persona and promotional savvy. An author, progressive organizer and advocate of Internet deregulation, Lessig’s won backing from such Silicon Valley heavyweights as Apple co-founder Steve Wozniak and PayPal co-founder Peter Thiel. His crowdfunding model — donors were told they would get their money back if the PAC didn’t meet its targets in time — went viral to draw in 53,000 contributors.

The constitutional amendment push has also fueled surprising popular support. The amendment proposed by New Mexico Democrat Tom Udall in the Senate and introduced this week in the House by Rep. John B. Larson, D-Conn., flies in the face of more than one landmark Supreme Court ruling. Republicans deride it as a blatant First Amendment violation.

Some campaign finance experts cast the uphill amendment drive as an ill-advised distraction from more pragmatic changes. Lessig’s Mayday PAC, for one, is focused not on amending the Constitution but on such changes as matching small-dollar donations with public funding. Yet proposals to amend the Constitution are now backed by 16 states and 550 municipalities.

“People are really angry about what’s happening in our democracy,” said Margrete Strand, executive vice president of Public Citizen. The push for an amendment is something that average voters can “understand” and “grab onto,” she added.

To be sure, voters are notoriously fickle when it comes to campaign financing. Gallup’s latest polls on the topic found that half of voters support government funding of elections, and 79 percent support limiting campaign receipts and spending. But Democrats’ perennial assaults on big money have repeatedly failed to help them at the polls.

Lessig has set out to prove the issue can fire up voters as well as donors, and Mayday PAC will announce a slate of at least five federal candidates on July 21. Whatever the merits and demerits of various campaign finance schemes, voters will ultimately have the last word.

“The only way to prove this is to do it,” said Lessig. “We can have all sorts of polling and science and focus groups. But the thing that counts in Washington is victory.”

Eliza Newlin Carney is a senior staff writer covering political money and election law for CQ Roll Call.