It’s big.

Representative John Lewis, an elder statesman from the civil rights era and one of Senator Hillary Rodham Clinton’s most prominent black supporters, said Thursday night that he planned to cast his vote as a superdelegate for Senator Barack Obama in hopes of preventing a fight at the Democratic convention.

“In recent days, there is a sense of movement and a sense of spirit,” said Mr. Lewis, a Georgia Democrat who endorsed Mrs. Clinton last fall. “Something is happening in America, and people are prepared and ready to make that great leap.”

Pair that move with Al Sharpton’s threat to march on the DNC if the Florida and Michigan delegates are seated, delegates without which it’s becoming apparent that Hillary can’t win the nomination, and you have a tectonic-scale move against her. But Tom Maguire makes a good point that Lewis’ endorsement helps Obama now more than it would have last fall.

I very much wonder whether a John Lewis endorsement of Barack would have been valuable to Obama last fall. Remember, Barack has been intent as presenting himself as something other than merely a black candidate (see the “Keep Hillary Alive” spin here); a string of early endorsements from prominent civil rights legends would have been counter-productive (although Oprah’s cross-over appeal was welcomed).

Indeed. Part of Obama’s appeal has been that he hasn’t hugged the Jesse Jacksons of the world. If he had, it would have limited his reach.

What the Lewis move adds to is the perception that momentum among the superdelegates is shifting toward Obama. Hillary is counting now on winning out the primaries starting with Texas and Ohio, seating the FL and MI delegates and keeping her hold on the majority of the superdelegates. That’s a weak strategy. Lewis’ shift says she isn’t keeping that hold now and is likely to lose more of them in a cascade effect. Not good for the Glacier’s prospects.

Update: From the comments, a reason to hold the phone? Is there campaign skulduggery afoot?

Update: The AJC says Lewis hasn’t switched.

Jones, Lewis’ spokeswoman, told the Washington Post that “it is plain there is a lot of enthusiasm for Barack Obama.” But, she said, “those things are observations,” not statements of preference. Jones told the newspaper that Lewis has left the option of changing his superdelegate support for Clinton on the table, but made no decisions.