The Nation -- Georgia Congressman John Lewis, the civil right movement veteran whose endorsement was once seen as a critical component of Hillary Clinton's appeal to African-American voters, confirmed on Wednesday that he will cast his superdelegate vote at this summer's Democratic National Convention for Barack Obama.

Lewis, who hinted at the shift several weeks ago after his Atlanta-area district voted overwhelmingly for the Illinois senator, has told the Atlanta Journal Constitution that, "It's been a long, hard difficult struggle to come to where I am. But when I am, as a superdelegate, I plan to cast my vote at the convention for Barack Obama."

"Something's happening in America, something some of us did not see coming," explained Lewis. "Barack Obama has tapped into something that is extraordinary.

The move costs Clinton more than just a prominent endorsement at a time when her campaign has suffered a number of setbacks, including last week's overwhelming loss in the Wisconsin primary.

It suggests that members of Congress who endorsed Clinton early but whose districts have since voted for Obama will come under increasing pressure to "keep faith with their constituents" by casting their superdelegate votes for Obama.

As Obama has surged, his support among superdelegates -- the almost 800 elected officials and party leaders who are guaranteed votes at the convention not by caucus or primary results but by virtue of their positions -- has grown dramatically.

With the Lewis move, the Illinois senator now has commitments from 201 superdelegates to 255 for Clinton. And the Illinois senator's base of support will almost certainly increase in coming days as members of Congress -- not just African Americans but white liberals who represent college towns and urban areas where Obama has run especially well in recent primaries -- are encouraged to follow the lead of John Lewis.

Lewis, who remains close to Clinton, is not expected to lobby his colleagues all that hard on behalf of Obama. Frankly, that won't be necessary. His decision says everything that needs to be said.[MORE]