“The country is not what it was,” sings a character in “Assassins,” and who’s going to argue with him, even if he is a homicidal maniac?

Like all plays, the Stephen Sondheim and John Weidman musical becomes as much about the time in which it’s performed as the time it was written (early 1990s). With its confusion about the ready availability of weapons and inattention to the problem of mental illness, as well as anger at a government that seems disinterested in providing for the needs of its citizens, “Assassins” feels of the moment. Left or right, we can agree that our country, tragically, is not what it was.

In the show, the line is sung by a triumphant John Wilkes Booth, shortly after killing Abraham Lincoln, and it comes at the climax of one of the most monumental numbers in all of musical theater, the soaring, nine-minute “Ballad of Booth.” Gorgeously sung and acted by Dieter Bierbrauer as Booth and Tyler Michaels as the narrating Balladeer, “Booth” lays out the assassin’s case with such passion and logic — a disastrous war, an unresponsive government — that we find ourselves sympathizing with Mr. Sic Semper Tyrannus, right up until the moment he makes a disastrous decision that changes the course of a nation.

That pattern is repeated in “Assassins,” in which we meet nine killers or would-be killers, arrayed on Eli Sherlock’s stunning and practical carnival set (arrive early so you can board it and play ring-toss with the cast). Like Sondheim’s “Company,” instead of a plot we’re given a series of vignettes in which a choral collective conscious — in this case, the nightmarishly warped hive mind of the assassins — unites to urge a protagonist to realize his dreams. Here, it’s Kennedy killer Lee Harvey Oswald (also played by Michaels), whose fatal act, the assassins insist, will make sure we remember them all. Throughout, director Peter Rothstein has the Balladeer stalk the theater, as if, like us, he’s trying to make sense of these troubled people.

“Assassins” is a painful show that asks us to confront the various ways in which our country has gone wrong, right up until its final, shocking image. It’s also a moving one, particularly when Oswald, Booth and Samuel Byck — whose Richard Nixon-hating character has never really made sense for me until this production, in the hands of James Detmar — are confronting their crimes.

It’s also a tuneful show, since each song hews to the time period of its crime. (John Hinckley’s and Squeaky Fromme’s lush “Unworthy of Your Love” is like a Carpenters song, if the Carpenters had been vicious psychos.) And it’s a surprisingly hilarious one. Weidman’s loose, fluid book gives each character vivid comic moments and the actors take full advantage, particularly Sara Ochs as Sara Jane Moore, who seems as baffled by her own klutzy actions as by those of her target, President Gerald Ford.

Rothstein deftly manages the shifting moods of this production by his Theatre Latté Da. His decision to go hard on the carnival theme — it’s not just a setting but a metaphor that weaves its way into every aspect of the show — pays off in a production that warns us that the people who are stealing our attention are hucksters, and we play along with their games at our own peril.