As you know, some Dems have joined Republicans in casting doubt on the Bowe Bergdahl swap. Senators received a classified briefing on the exchange on Wednesday. But some left early, and some continued to express skepticism about the deal, suggesting the administration hadn’t proven that failure to act fast would put his life at risk, that the release of the Taliban five endangered national security, or that maybe Bergdahl, an alleged deserter, didn’t deserve to be saved.

To be sure, some Dems have raised legitimate questions about the legality of the swap. But others have offered half-baked responses that seem motivated by politics. As a New York Times editorial puts it, “fearful Democrats” have been just as quick in resorting to a “duck and cover response,” and just as quick to jump on the anti-Bergdahl “bandwagon,” as Republicans have been. For instance, Joe Manchin opined: “I think we can all agree we’re not dealing with a war hero here.” Okay, and that tells us what, exactly?

Senate Dems in particular should do better. We need to hear serious, coherent arguments from them as to why they think this deal either was — or wasn’t — the right thing to do, within the boundaries of what classification permits.

Luckily, some Senate Dems — and Republicans, if they are up to the challenge — will have another chance to do just this. They will have another chance to learn still more about Bergdahl and the circumstances surrounding the exchange, because the Senate Armed Services Committee, which includes two dozen Senators, is holding another classified briefing next Tuesday, at which they will be able to quiz Deputy Secretary of Defense Robert Work and Joint Chiefs vice chairman James Winnefeld, among others.

Here’s a hint as to where that could lead.

I’m told that Senator Carl Levin, the chairman of Armed Services, called Winnefeld earlier this week to ask a pointed question: Do senior military officials really stand by this swap? The Senator’s hinted implication, a source familiar with the conversation says, was to ask: Are they just taking one for the President?

Obama has defended the exchange by arguing: “We have a basic principle. We do not leave anybody wearing the American uniform behind.” Levin asked Winnefeld whether military leaders really believed that this core principle was at stake here. According to the source, Winnefeld’s answer was an unequivocal Yes.

This is a line of questioning that Senators on Armed Services — from both parties — can pursue on Tuesday. And there’s more. We now have a significantly more nuanced understanding of Bergdahl and the swap than we did at the time of the initial briefing of Senators on Wednesday. For instance, the narrative was previously dominated by charges, first made by soldiers in interviews with CNN’s Jake Tapper, that Bergdahl was a deserter who may have tried to link up with the Taliban. But we have since learned that an internal military report completed just after Bergdahl disappeared in 2009 casts at least some doubt on both of those notions, though they could both still be true.

What’s more, a former military official has since explained to Tapper that even if Bergdahl did seek out the Taliban, he could have had a motive other than treachery, such as a “messianic mission on his part to stop the violence and perhaps help broker an understanding with the local Taliban.”

We have also since heard from a senior administration official that the exchange had to be kept secret from Congress out of fears that a public leak could lead Bergdahl’s Taliban captors to kill him, in part because of a split among the Taliban about the wisdom of the deal. If true, that rationale goes well beyond the belief that Bergdahl’s deteriorating health required rapid action (which Senators have not found persuasive, based on video evidence).

The point is that we know a lot more now — and we have a much better sense of what we do not know — than we did earlier this week. And in the coming briefing, Senators can press for more information on the true nature of the proclaimed threat to Bergdahl’s life, on what is really known about his conduct, and on the core principle that senior military officials apparently believed was at stake.

To be sure, Senators will be limited in what they can tell us, thanks to classification. And it’s also possible that, after the coming briefing, Senators will still remain unconvinced that the circumstances justified the illegality of the swap under the administration’s claim of a Constitutional obligation to save his life. That’s fine. What we really need to hear is evidence that Senators did all they could to fully understand the true nature of the decision the administration faced — as well as serious, coherent explanations for their conclusions about it.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.