There's a deliciously snarky line in Harry Reid's memoir about life in the U.S. Senate. Take a guess who's deemed to be snark-worthy.

While recounting an '07 legislative campaign by Senate Democrats to reverse President Bush's Iraq war policy, the Majority Leader writes about his fruitless outreach to the Republicans. Reid needed the votes of at least a few GOP senators, but they kept jerking him around. Then he writes: "Several were publicly wavering. And some were consistently sending signals that they were with us, but when it came time to vote, they were not. Arlen Specter of Pennsylvania is always with us when we don't need him."

The question many Democrats are asking themselves today is: Will Arlen Specter be with us when we need him?

Democrats may well be tempted to respond in the negative. Specter, in his first week as a Democratic senator, has done the following:

1. He voted against the Obama budget.

2. He restated his opposition to a landmark labor reform bill that would make it easier for unions to organize workers.

3. He said that he will oppose the confirmation of Dawn Johnsen, an outspoken critic of the Bush torture memos and currently the president's choice to helm the Justice Department's critically important Office of Legal Counsel.

4. He told NBC that his new party colleagues should not automatically count on him for anything: "I did not say I would be a loyal Democrat."

5. He said that he opposes another key Democratic proposal that would give people the option of singing up for public health care.

6. He said that, in the name of "justice," he supports Republican Norm Coleman over Al Franken for the Minnesota Senate seat, even though Franken has already been declared the winner in a statewide hand recount and again in a court ruling by a bipartisan trio of judges.

Given all those developments - and the results of a Washington Post survey showing that Specter, all told, has voted with the GOP 65 percent of the time - it's no wonder that many grassroots Democrats are thirsting to challenge Specter in the 2010 Senate Democratic primary. They'd love to see a well-financed candidate who would contest Specter from the left; in fact, for a Specter challenger running in a Democratic primary, that NBC video clip ("I did not say I would be a loyal Democrat") could be the political equivalent of chocolate cake with a cherry on top.

The problem, however, is that Democratic leaders, starting with Obama, are working hard to clear the field for their incumbent convert, regardless of grassroots sensibilities.

You almost have to feel sorry for Joe Sestak, the Democratic congressman from the Philadelphia suburbs, a former vice admiral who had been gearing up to run for the Democratic nomination prior to the Specter switcheroo. He even has $3 million in his campaign kitty, ready to go. Scant weeks ago, he was being wooed for the job by the Washington Democratic leaders...but now he's being screwed by the Washington Democratic leaders. Suddenly, they're telling him that it's Not His Time. Overnight, they've become ardent for Arlen.

Sestak may ultimately play the good soldier and bow to the pressure. But not just yet. For now, he's just about the only prominent Democrat willing to fire away at Specter. On Monday night, he told a liberal website that Specter's decision to switch parties was symptomatic of a character flaw: "He left the fight. In the military, we just don't leave fights." Sestak also zapped the party leadership: "It isn't Washington's prerogative to tell us what to do."

Sestak said something similar on the radio yesterday: "The reason I got into politics was not to have the establishment reestablish the establishment." Not a particularly eloquent remark, but you get the idea. And over the weekend, he skewered Specter on CNN: "I'm not sure he's a Democrat yet." With no need to make a final decision just yet, Sestak has some time to take his shots, assess the reaction, watch and wait, and (most importantly) see how Specter actually votes when the chips are down.

There are many voices of discontent. Former party chairman Howard Dean, presumably speaking for what he once called "the Democratic wing of the Democratic party," said the other day that "you don't clear the field in a place like Pennsylvania, you only clear the field by merit." Meanwhile, labor leader Andy Stern met Monday with Sestak and let it be known that he considers Sestak "impressive." (Labor has a lot of clout in a Democratic primary.)

Elsewhere, a nascent Draft Sestak movement is being launched in the liberal blogosphere. Some prominent liberal bloggers have also formed Accountability Now PAC, which believes that party primaries should be contested - and offers Pennsylvania as Exhibit A: "We oppose ongoing efforts to deny Pennsylvania Democrats their right to choose who represents them in the Senate." And at least once declared Democratic candidate, Philadelphia civic leader Joe Torsella, is vowing to stay in the race and fight Specter in the primary.

But with Obama, Joe Biden, and Ed Rendell applying the pressure on Specter's behalf, it's likely that Torsella's money will dry up; at best, he seems fated to be the token candidate for aggrieved liberals - the same role played by Philadelphia lawyer Alan Sandals during the '06 Democratic primary that Bob Casey won handily.

So at this point, it's hard to see how the liberal base can rise up and deny Specter the '10 nomination. And, for the party, this could prove to be a mixed blessing - given the fact that Specter is such a high-maintenance guy. As the New Republic magazine warned in an editorial the other day, "If Obama and other Democrats allow Specter to switch his party simply to get reelected without switching his votes, then their marriage with him will be loveless - and they will be trapped in it."

And speaking of high maintenance...remember how I mentioned, a bit earlier, that Specter had declared his support for Republican Norm Coleman in the Minnesota Senate race? That remark appeared online yesterday in a New York Times Magazine Q & A. But now, Specter is suddenly renouncing his support for Coleman. Now he's telling Congressional Quarterly: "In the swirl of moving from one caucus to another, I have to get used to my new teammates. I'm ordinarily pretty correct in what I say. I've made a career of being precise. I conclusively misspoke."

"In the swirl of moving," he apparently forgot to flip flop.

Rarely has a politician been so open and honest about being so conviction-free.