“Lions for Lambs” marks another installment in the series of movies about our current national nightmares. It comes on the heels of “In The Valley Of Elah” and “Rendition,” which examined the traumas of war and America’s use of torture, respectively. “Lions” takes a step back to challenge the national character during the “War on Terror.” It has the finest pedigree of the three, with Robert Redford directing and starring along with Tom Cruise and Meryl Streep DRA ’75, and it wants to serve as a call to arms to stand up and fight for what’s right. Too bad it lacks the guts to ask anything challenging of its audience or its characters. “Lions” is ultimately a hollow venture that wants us to lap up its mushy liberalism while forgetting the fact that, for the most part, it neglects being a good movie or having a sharp political message.

Redford cuts between three storylines. Streep plays Janine Roth, a journalist who interviews Sen. Jasper Irving (Cruise) in his chambers about his “new strategy” for the war in Afghanistan. At the same time, Prof. Stephen Malley (Redford) meets with a student (Andrew Garfield) in his office to lecture him about his apathy. Two of his former students, Ernest (Michael Pena) and Arian (Derek Luke), now soldiers, languish on a bleak, snow-covered Afghani mountain.

The boldest thing about “Lions for Lambs” is its construction. It’s talky enough to be a play and barely moves from its three main locations. There aren’t many movies this content with staying put. The characters mostly sit and talk. Occasionally, one of them leaves the room.

A movie that is all script had better have a good one, but “Lions for Lambs” does not. Screenwriter Matthew Michael Carnahan produces an endless parade of familiar phrases that, while well-written, rarely say anything new or deeply examine where America is now. The past six years have given Carnahan a lot of material to work with, but he is content to stay within the lines. Iraq didn’t attack us, Streep says. We face an evil threat, Cruise says. Remember to get involved, Redford says.

The filmmakers are tapping into unhealed wounds here, going after an administration at the height of its unpopularity. It’s easy to get fired up in the moment, but “Lions” dissipates the second the credits roll. Even in a notably heated portion of the debate between Streep and Cruise, the most probing and provocative question — “Since when has America been a force for righteousness?” — is left buried and unanswered, easy to miss if you’re not paying close attention. Why bother to ask the tough questions when you can coast on the easy ones?

This is not to say that everything is dull. Listening to Cruise and Streep battle it out is by far the best part of “Lions for Lambs.” Streep runs away with the movie. She has the best role, if only because Carnahan seems to have taken the time to give her a real human being to play, a luxury he does not give anyone else. She listens to Cruise’s highly dubious — and likely immoral — plans for his strategy with increasing anger and a determination not to screw up as much as she did in the run-up to Iraq. Cruise is no match for Streep, but he’s very effective in a role that suits his particular brand of snake-oil charm. The problem is that he’s a construction, not a character; he’s a man composed entirely of the verbal detritus of the GOP and not one with a real personality.

Cruise and Streep’s dialogue is fun because it’s a concise and well-acted summation of the debate we’ve been having since the war began. But Redford seems afraid to go too far, to say anything that is not broadly popular. At this point, how hard is it to say that things have gone horribly wrong?

Malley and his students suffer from the same lack of care as Cruise. They all feel like perfectly balanced stick figures, designed not to ruffle any feathers. Malley doesn’t want Ernest and Arian to join the military, but he served in Vietnam, so he’s still a patriot who loves our troops. The two students are black and Latino, from “rough neighborhoods.” (The movie helpfully flashes one’s Compton address.) They think there’s a lot wrong with America, but they still love it enough to enlist, and who can disagree with that? We huddle with them in the Afghani winter, but we’re not supposed to like them for anything other than what they represent. Race and class are not used to further their characters, but rather to increase their sainthood. It’s disingenuous and icky.

There is only one time when “Lions” reaches beyond the mediocre. At the end, Streep has a bravura scene where she unloads all of her complicity in the war, calling the whole thing “bullshit.” There’s a lot of swearing in “Lions for Lambs,” but that “bullshit” is the only one that sticks, because it has something real behind it. It’s a scene that is nothing like the rest of the movie — full of passion and complexity, a welcome howl of a polemic that breaks away from Carnahan’s otherwise measured tones and speaks in a way that we might not hear on TV.

The tagline for “Lions for Lambs” is “If you don’t stand for something, you might fall for anything.” It’s a message the filmmakers would have been wise to heed.