Benjy Sarlin for MSNBC:

While both Bush and Rubio have said they favor more transparency in campaign finance (Bush has floatedallowing unlimited campaign donations, but disclosing them within 48 hours online), neither has publicly called on groups supporting them to disclose their backers or explicitly called for a law that would compel them to do so.

Until now, at least: Asked in an e-mail by msnbc whether Bush’s proposed solution would include legislation to “bar outside groups supportive of a candidate from raising money anonymously” Miller answered in the affirmative.

“Ya he would support a law that would increase transparency and disclosure,” Miller said.

A spokesman for Every Voice, an advocacy group that favors further transparency in campaign finance, hailed the news while calling on Bush to provide further details.

“If this is what the Bush campaign means by ‘commitment to transparency,’ we’re happy to see it,” Adam Smith, communications director at Every Voice, told msnbc. “There are plenty of things that can be done, both through legislation and the regulatory process, to increase transparency in political spending and I’d love to see what he’d support if elected.”