David Corn is as left wing as you can be and still be considered mainstream.
Here's David Corn in Mother Jones today:
When Specter last year bolted the Republican Party and became a Democrat — when it looked as if he might not be able to win the GOP primary — the White House said that he would have its full support.http://motherjones.com/mojo/2010/05/specter-loss-obamas-word-not-so-good
. . . For months, Specter — a politician with much name recognition in the Keystone State — looked like a good bet for the White House. He maintained a double-digit lead over Sestak. But in the final weeks of the campaign, Sestak drew to a tie in the polls.
. . . But with the race close, the White House did nothing special for Specter. President Barack Obama recorded one robo-call. Neither he nor Vice President Joe Biden campaigned with Specter. It appeared that they had cut him loose. It wasn't pretty.
. . .Obama's pirouette in Pennsylvania made political sense. But did Obama send a signal: don't trust me? He had said he would put his muscle behind Specter, but in the end he didn't. This might have been best for the party, for Sestak could well be the better Democratic candidate in the general election. And if Sestak wins in November, what Obama did with (or to) Specter won't matter much. For now, though, this one race shows that Obama's endorsement doesn't have much juice (ask Martha Coakley and Jon Corzine about that) and that any promise of support from Obama is vulnerable to political calculation.
If the hard core of Obama's base believes Obama's word is "not so good", it's going to be hard for Obama to get anyone to trust him.