There are several legislative proposals that would accomplish parts or all of what the Mayday PAC seeks. David Price, a North Carolina Democrat, has introduced a bill to provide public financing for congressional races; it has 28 Democratic and one Republican as co-sponsors. A proposal from the Maryland Democrat John Sarbanes would provide a 50 percent tax credit for individual campaign contributions to House candidates and national parties and create a voucher program that would enable individuals to give up to $50 in contributions to candidates. That bill has 156 cosponsors, including one Republican. Another proposal by Mr. Sarbanes would provide a $25 tax credit for making certain campaign contributions and has attracted 43 Democrats.

These bills speak to three larger truths. First, even among House Democrats, there isn’t a single idea or legislative proposal that has captured broad support within the party, to say nothing of Republicans. The campaign finance law passed in 2002 was several years in the making and required the support of 41 House Republicans, who helped bring the bill to the House floor.

Second, a public financing plan, if enacted, would not do anything to curb the influence of super PACs, which were created not by Congress but through the courts, including the Citizens United decision. While there is an attempt in the Senate to pass a constitutional amendment to give Congress and the states the authority to regulate independent spending, even the Mayday PAC describes this as unlikely and possibly unnecessary.

Third, while there is support among the public for a public financing system -- a 2013 Gallup poll found that half of Americans would personally vote for a law creating one -- that support was much higher among Democrats than Republicans or independents, and least in the South and West, where it did not command majorities. Securing victories against incumbent Republicans would require energizing and turning out independents in November. The same poll found greater levels of support for limiting the amount of money candidates could raise and spend.

Appeals for the Mayday PAC have been scrupulously bipartisan, with complaints about money’s impact on both the right and left. But a map of the number of donations to the Mayday PAC through June 27 shows more donations from areas where Democrats are already representing congressional districts, mainly cities on the east and west coasts and urban centers in other states.

The geographic source of the money won’t matter much in independent spending campaigns, but when it comes time to vote, the harder task will be connecting with potential voters for whom the issue of campaign finance rivals health care, taxes or the economy.

Mayday PAC acknowledges the difficulty it faces, even while placing an emphasis on actually winning this year: “It is our view that to win on this issue ultimately, we will need to identify new techniques that can bring new voters into the political process. But in the short term, we need to use whatever techniques we can to win.”