On his Pmarca blog today, Marc Andreessen comes out in support of Barack Obama in the race for the Democratic presidential nomination. Andreessen bases his endorsement on a private 90-minute meeting last year in which, he says, Obama "grilled him" on the impact social networking would have on politics.

Andreessen's post comes just a day before primaries in Texas, Ohio, Rhode Island, and Vermont that could determine whether Obama or Hillary Clinton represents the Democrats in the fall election. Andreessen says he has "tried very hard" to stay away from politics on his blog, then jumps in with both feet. "He's got my vote," he says of Obama.

Andreessen reflects back on a meeting that took place nearly a year ago. That's a long time ago in the current political scene, but Andreessen thinks it has value in showing what Obama was like before he was fully engaged in today's race. "I think we got a solid look at what he's like up close," says Andreessen.

The subject of social networking came up, not surprisingly given Andreessen's involvement with Ning. "The Senator was personally interested in the rise of social networking, Facebook, YouTube, and user-generated content, and casually but persistently grilled us on what we thought the next generation of social media would be and how social networking might affect politics," Andreessen writes.

What might that look like in action? On Ning, a half-dozen social networks have been created by Obama supporters, including Families for Obama, Obama-nation, and Obama Friends. A Ning search for Hillary Clinton comes up empty.