A few months ago, when Rep. John Lewis (D-Ga.) endorsed Hillary Clinton, it was a key development. Lewis, a Democratic icon and civil-right legend, became Clinton’s highest-profile African-American supporter, and sent a signal to the party about Clinton’s strong connection to the African-American community.

As I understand it, Lewis was, a few months prior, undecided on whether to support Clinton or Barack Obama, but cajoling from Bill Clinton reportedly pushed the Georgia congressman into Sen. Clinton’s camp.

Now, it appears circumstances have pushed Lewis in the other direction.

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.”

Mr. Lewis, who carries great influence among other members of Congress, disclosed his decision in an interview in which he said that as a superdelegate he could “never, ever do anything to reverse the action” of the voters of his district, who overwhelmingly supported Mr. Obama.

“I’ve been very impressed with the campaign of Senator Obama,” Mr. Lewis said. “He’s getting better and better every single day.”

Time’s Mark Halperin argued that Clinton’s chances of winning the Democratic nomination, in light of Lewis’ announcement, have been cut in half. That strikes me as a bit of an exaggeration, but I think it’s certainly fair to say this is a major development.

Right off the bat, it’s worth remembering that not all superdelegates carry equal stature and credibility. Lewis is one of the most respected and admired lawmakers in the party. He carries enormous, almost unrivaled, moral authority, and his switch may very well lead others to do the same.

Moreover, it leaves the Clinton campaign’s broader superdelegate strategy looking suspect. The principal reason to distrust the superdelegate counts we see in the media is that these are people who haven’t actually voted yet. They can, and will, change their minds, and are susceptible to prevailing political winds and shifts in momentum. It’s obviously too soon to say, but Lewis’ announcement may signal a break in the dam.

The Clinton campaign has suggested in recent days that the superdelegates would be their ace in the hole. That may no longer be the case. Josh Marshall explained:

The Clinton camp’s super delegate gambit is not only audacious. Far more than that it is simply unrealistic. The super delegates who are gettable for Clinton by loyalty, conviction or coercion are already got. And enough’s been seen of both candidates for everyone to be more than acquainted with them. The ones who remain — who make up roughly half the total — are waiting to see who the winner is.

The truth is that there are over 1000 elected delegates remain to be won. We really don’t know what’s going to happen yet. But if the trend continues and Obama ends the primary season with a clear majority of unelected delegates, the idea that those remaining super delegates will break for the candidate who won fewer delegates, raised less money and is polling worse against the Republican nominee simply makes no sense.

My hunch is this hurts Clinton most because it seems to represent a tipping point. To be sure, it may not be, but that’s certainly the perception that many Democrats may have this morning. The post-Super Tuesday period has been an awkward one for her campaign, between a string of defeats and a significant staff shake-up. But there was also a sense that, if Clinton could keep her team together and focus on some likely victories down the road, this unpleasant streak could pass.

Lewis’ move, in this sense, signals that time may not be on Clinton’s side.

From crooks & liars.