The Pennsylvania Democratic primary for the U.S. Senate, which pits cranky incumbent Arlen Specter against cranky challenger Joe Sestak, has divided key players in the party coalition, with labor unions and women’s rights, gay rights and civil rights lining up on both sides of the fight. So be it. That’s the whole point of a primary.

No doubt, Sestak is running a more energetic and appealing campaign.

And he is certainly benefiting from the fact that Specter sometimes forgets he is now a Democrat, as the party-switching senator recently confirmed when he accepted an important endorsement. "I thank the Allegheny Republican Committee for endorsing me for the Democratic nomination … great pleasure to be endorsed by the Allegheny County Republicans and together we’ll win for victory, for a better state, for a better nation," the senator chirped.

Unfortunately, it was the Allegheny County Democratic Committee, not the Republican one.

As someone who wrote for some years about politics for the Pittsburgh Post-Gazette, I can tell you that such missteps are noted.

Sestak quicker on his feet. But the congressman’s over-the-top support for the occupation of Afghanistan offers a reminder of the extent to which he really does not "get it."

While President Obama is backing Specter—in what can best be described as payback for the senator’s party switch—it is Sestak who usually goes off the deep end when it comes to positioning himself as handmaiden for the White House.

Specter, irrascible as ever, accepts the president’s endorsement and then raises objections about Obama’s foreign and domestic policies—many of them apt.

The wrangling about who is going to be the better backer of the White House came to a head when Obama nominated Solicitor General Elena Kagan to fill the seat Justice John Paul Stevens will leave on the Supreme Court bench.

Sestak made a big deal about the fact that Specter had voted against confirming Kagan to serve as Solicitor General.

In a particularly snarky statement released after Kagan was nominated, Sestak grumbled: “My opponent, Sen. Specter, has already made his views about the president’s nominee clear by voting against her confirmation to be solicitor general, even as seven of his fellow Republicans approved her nomination,” Sestak said in a statement. “I expect Sen. Specter may backtrack from his earlier vote on Ms. Kagan this week in order to help himself in the upcoming primary election, but the people of Pennsylvania have no way of knowing where he will stand after May 18.”

The intimation was that Sestak would just jump on board the Kagan bandwagon, no questions asked, while Specter could not be relied upon to rubberstamp it.

To his credit, Specter did not backtrack.

He said:

“There is no doubt that Elena Kagan has exemplary academic and professional credentials. And she has been a pioneer for women, serving as the country’s first female Solicitor General and as the first woman to be Dean of Harvard Law School. I applaud the President for nominating someone who has a varied and diverse background outside the circuit court of appeals.

"I voted against her for Solicitor General because she wouldn’t answer basic questions about her standards for handling that job. It is a distinctly different position than that of a Supreme Court Justice.

“I have an open mind about her nomination and hope she will address important questions related to her position on matters such as executive power, warrantless wiretapping, a woman’s right to choose, voting rights and congressional power."

Even senators who disagreed with Specter’s vote against Kagan for Solicitor General recognized that it was based on reasonable concerns. Kagan was not particularly cooperative when she testified before the Judiciary Committee early in 2009. Senators on both sides of the partisan aisle were frustrated with her failure to answer questions that really should have been answered—especially at a time when Obama was promising a more open and transparent administration that would display a far higher regard for the Constitution and the rule of law.

Specter summed up the concerns when he said in 2009:

"I have gone to really great lengths to find out about Dean Kagan’s approach to the law and approach to the job of Solicitor General and to get some of her ideas on the law because she’s in a critical public policy making position. I had the so-called courtesy visit in my office which was extended as the Ranking Member on the Judiciary Committee. We had an extensive hearing where I questioned her at some length. Written questions were submitted and she responded to them. I was not satisfied with the answers which were given and when her name came before the Committee, I passed. That means I didn’t say "aye" or "nay." But I wanted to have her nomination reported to the floor so we could proceed, and I wanted an opportunity to talk to her further and did so earlier this month. I wrote her a letter asking her more questions and got some more replies. And I use the word replies carefully, because I didn’t get too many answers as to where she stood on some critical issues. After the long process I have described, I still don’t know very much about Dean Kagan.

"I have no illusion that the issues that I have raised will prevail. I think it is pretty plain that Dean Kagan will be confirmed. But I do not articulate this as a protest vote or a protest position but really one of institutional prerogatives that we ought to know more about these nominees; we ought to take their confirmation process very seriously.

"I think we have to pay a little more attention, and I’ve gone to some length to try to find out more about Dean Kagan. But in the absence of being able to do so and really have a judgment on her qualifications, I’m constrained to vote no."

As Specter and other members of the Judiciary Committee consider the Kagan nomination, they have a responsibility to ask tough questions and demand reasonable cooperation. This is especially true of Democrats on the committee, as they have proven to be the stronger advocates for checks and balances and the separation of powers in recent years.

Specter’s determination to question Kagan about "on matters such as executive power, warrantless wiretapping, a woman’s right to choose, voting rights and congressional power" mirrors that of Democrats such as Wisconsin Senator Russ Feingold, the chair of the subcommittee on the Constitution.

Instead of playing political games, Sestak should be complimenting Specter for doing his job—and for obeying his oath to defend the Constitution.

There are plenty of legitimate reasons to criticize Arlen Specter, and there is nothing wrong with Sestak highlighting those criticisms.

But with regard to the Kagan nomination, Specter’s skepticism is appropriate. Chances are that Specter will vote to confirm Kagan. But we should all hope that he and other Judiciary Committee members ask aggressive and detailed questions about executive power, warrantless wiretapping, a woman’s right to choose, voting rights and congressional power before rendering their judgements.