Stanley Kurtz lays it all out in an article in the current issue of National Review which he summarizes in a post at National Review Online.
The party is the New Party, and though there's nothing illegal about having been a member, there's something disreputable about having persistently denied one's affiliation and having tried to hide that connection from the American electorate. It's just one more indication that Mr. Obama is not the man he wanted the American public to think he was during the 2008 campaign.
Here's Kurtz' lede:
On the evening of January 11, 1996, while Mitt Romney was in the final years of his run as the head of Bain Capital, Barack Obama formally joined the New Party, which was deeply hostile to the mainstream of the Democratic party and even to American capitalism. In 2008, candidate Obama deceived the American public about his potentially damaging tie to this third party. The issue remains as fresh as today’s headlines, as Romney argues that Obama is trying to move the United States toward European-style social democracy, which was precisely the New Party’s goal.Perhaps Mr. Obama is not a socialist, but just thought it'd be fun to become a dues-paying member of the socialist party. Who knows?
In late October 2008, when I wrote here at National Review Online that Obama had been a member of the New Party, his campaign sharply denied it, calling my claim a “crackpot smear.” Fight the Smears, an official Obama-campaign website, staunchly maintained that “Barack has been a member of only one political party, the Democratic Party.” I rebutted this, but the debate was never taken up by the mainstream press.
Recently obtained evidence from the updated records of Illinois ACORN at the Wisconsin Historical Society now definitively establishes that Obama was a member of the New Party. He also signed a “contract” promising to publicly support and associate himself with the New Party while in office.
Minutes of the meeting on January 11, 1996, of the New Party’s Chicago chapter read as follows:
Barack Obama, candidate for State Senate in the 13th Legislative District, gave a statement to the membership and answered questions. He signed the New Party “Candidate Contract” and requested an endorsement from the New Party. He also joined the New Party.Consistent with this, a roster of the Chicago chapter of the New Party from early 1997 lists Obama as a member, with January 11, 1996, indicated as the date he joined.