The teetering public campaign finance system loses another Jenga block as Barack Obama opts out of it for the general election.

"We’ll be forgoing more than $80 mil in public funds," he said, adding that while he supports a "robust" public system, "the public financing of presidential election as it exists today is broken and we face opponents who have become masters at gaming this broken system."

"We’ve already seen that [McCain] is not going to stop the smears and attacks from his allies running so-called 527 groups who will spend millions and millions of dollars in unlimited donations," he said, though  the only well-funded independent attack ads, from MoveOn.org, have been directed at McCain.

This is a "king of the beach" moment for Obama, who has been cajoled, hectored, and begged by John McCain not to opt out, and to accept the fundraising cap that comes with federal cash. But McCain gave Obama the fig leaf for this six years ago when McCain-Feingold sent big money surging into 527 groups. Obama weasled out of his stated desire to accept public financing by saying that he'd only take it if Republican 527s were muzzled—an impossible demand. I expect McCain to attack Obama over this, but it's a sucker's issue. What more proof do voters need that McCain's signature accomplishment of the last decade was a bust.

I pre-emptively started shoveling dirt on public financing last year, back when McCain was taking the same position as Obama.