Presidential candidate Bernie Sanders is prepping a new proposal for campaign finance, he told Vox in a recent interview. And one big idea he's considering would give every US citizen some money to donate as he or she chooses.

"One way which I find intriguing is that you basically provide $100 for every citizen in the United States of America, and you say to that person, 'Here's your hundred bucks, you can make a contribution, you can get a $100 tax credit if you spend $100 on any candidate you want,'" Sanders said. "I think that would democratize very significantly the political process in America and take us a long way away from these Super PACs controlled by billionaires who are now buying elections."

Sanders suggested that details on his own plan would come later. But his shout-out gives a boost of attention to the tax credit idea, which has been floating around the campaign finance reform world in recent years as a potential way to counterbalance the influence of big money on the political process.

It's an attractive idea for campaign finance reformers — both because they think it's good policy, and because they think it could pass muster with the conservative Supreme Court. But it will be difficult to pass through Congress, where only one Republican has signed on. And some critics think that amplifying the power of small donations could lead our politics to become even more polarized.

Tax credits for small campaign donations actually existed just 30 years ago. As David Gans of the Constitutional Accountability Center explained in a useful briefing, a 1971 law created a tax credit for half the value of small political donations. At first, the credit's maximum amount was $12.50 (for any individual who gave at least $25 in contributions). Later it was increased to $50 for individuals and $100 for joint filers. But the 1986 tax reform law wiped it out, as it tried to raise revenue by repealing various credits and deductions.

Now, with the vast sums of money pouring into elections during the Citizens United era, some people want to bring it back. Rep. John Sarbanes (D-MD) has taken the lead in Congress with his Government by the People Act. His bill would give a tax credit for the value half of donations to US House candidates, up to a maximum value of $25 for individuals. Sanders is co-sponsoring a similar bill in the Senate, aimed at that chamber's elections.

Of course, making small donations easier wouldn't necessarily be enough to match up to the huge outside spending by millionaires and billionaires, as Sanders acknowledged to Vox. "I think what you want to do is at least make sure that candidates who are running will have as much money as their opponents — who may have unlimited sums of money," he said.

That's why Sarbanes's bill provides a way for the power of small donations to be amplified. If candidates foreswear accepting contributions of more than $1,000 from any individual (the current maximum is $2,700 per election), smaller contributions of up to $150 each would be matched with six times that amount in public funds. So a donation of $100 would be matched with $600 in public money, making each one worth $700 overall.

The public funds would only be available to candidates who first demonstrate local grassroots support by raising $50,000 from at least 1,000 donors in their states — thus preventing the matching funds from going to complete fringe figures. The candidates who accept these matching funds could then get even more if tons of late outside money pours in against them.

Sarbanes's bill has been very popular among House Democrats, but of its 151 co-sponsors, only one is a Republican. That's no surprise — campaign finance has become an intensely polarizing issue at the national level, with Democrats overwhelmingly supporting more restrictions and Republicans saying they're worried about chilling free speech. The benefit of Sarbanes's bill is that it doesn't block anyone's speech specifically — rather, it helps small donors' speech be heard. Still, any new campaign finance legislation faces a tough road ahead in a GOP-controlled Congress. (Rep. Walter Jones of North Carolina is the only Republican to sign on so far.)

There are also questions about whether amplifying the power of small donations could end up polarizing our politics even more. The candidates who raise lots of small dollars are usually at the left and right edges of their parties, as Adam Bonica and Jenny Shen wrote at the Monkey Cage. Recent small-donor successes include Ben Carson, Michele Bachmann ... and Bernie Sanders, who raised $10 million of his $13.5 million presidential fundraising haul from small dollars.

For now, Sanders is going to keep focusing on the campaign finance issue in his presidential campaign, just as he has for years. "The millionaire class and the billionaire class increasingly own the political process, and they own the politicians that go to them for money," he told Vox. "I worry very much, and I say this from the bottom of my heart, that we are moving very, very quickly from a democratic society, one person, one vote, to an oligarchic form of society, where billionaires would be determining who the elected officials of this country are. I'm going to do everything I can to stop that."