When Larry Lessig succeeded in raising $5 million for his Mayday PAC — giving him a total of $12 million for his campaign to limit the power of big money in politics — I argued that his big challenge will be finding Republicans willing to support his proposals. Today Lessig announced the first two candidates who will receive support from the Mayday PAC. The choices illustrate just how difficult it is to find credible Republican candidates who will support public financing of elections.

In Iowa, the Mayday PAC is supporting Democrat Staci Appel for Iowa's third district. It's easy to see why Mayday chose Appel — she's the only Democrat running for an open seat, and the district is evenly divided between Republicans and Democrats. Appel has an decent chance of winning, and if she does people are likely to cite Lessig's PAC as a significant factor.

In contrast, the Mayday PAC's choice in New Hampshire, Jim Rubens, is a long shot. He's a Republican candidate for US Senate. The most recent poll shows him running third in the Republican primary against former Massachusetts Sen. Scott Brown — by a margin of 61 percent to 10 percent. No poll has shown him with more than 12 percent of the vote, or doing better than third.

That's a big gap. And it's not obvious that buying a bunch of ads touting Rubens's support for publicly-financed campaigns can close it. Republicans in New Hampshire are more liberal than Republicans in some other states, but it's likely that many of them share the conventional conservative skepticism about public financing of campaigns.

Of course, Lessig doesn't have much choice. His campaign needs broad bipartisan support if it's going to overcome the entrenched interests opposing publicly-financed elections. And Rubens may have been the most promising Republican candidate the Mayday PAC could find.

Also, beating Brown would have symbolic importance for campaign finance reformers. When he was a Senator from Massachusetts in 2010, they lobbied him aggressively to support the DISCLOSE Act. The legislation failed to clear a filibuster by one vote, after Brown decided to vote no along with his Republican colleagues.

On the other hand, the fact that Rubens is such a long shot means that an upset victory would be a huge boost to the Mayday PAC's cause. And New Hampshire allows independent voters to vote in primaries. That could allow Rubens to win even if he can't win over hard-core conservatives. But picking him as the Mayday PAC's first Republican is a big gamble.