Jack McCallister (Matt Long) is a good-looking, popular, shallow, athletic teenager obsessed with women. His younger brother, Bobby (Logan Lerman), is a dorky, asthmatic Mama’s boy obsessed with starting a space club.
   One of them will grow up to be president of the United States.
   Part of the pleasure of the premiere of the WB’s promising new series, “Jack & Bobby”—which, true to the network’s word, is not about the Kennedys—comes from trying to figure out which one it will be.
   The show, premiering Sunday at 9 p.m., is set in present-day Missouri, with flash-forwards to 2049, when various talking heads—pundits, professors, the former first lady—offer their reminiscences about “President McCallister.”
   Only near the end of the hour do we finally learn which one will in fact ascend to the White House.
   On the surface, “Jack & Bobby” is a well-acted, heartfelt, but basically generic soft-focus WB drama about the bond between two very different brothers. It’s also about the influence of struggling single mom Grace (Christine Lahti)—she’s a strict and controlling university professor, but she smokes pot in the house to cope with stress—on her sons.
   Because this is the WB, it’s also about teen romance. In the premiere, Jack falls for standoffish Courtney Benedict (Jessica Pare), the daughter of a man Grace dubs “the money-grubbing whore.”
   But the future-POTUS twist, which seems at first like a mere clever gimmick, sets the show apart from “Summerland,” “One Tree Hill” and all the other forgettable WB mini-hits.
   The hints and suggestions of what happens in the years between now and 2049 give the present action far greater resonance. As we find out which brother becomes president, for example, we learn that the other died years earlier. Immediately, the relationship we’re watching build between the brothers takes on added depth and poignancy.
   “Jack & Bobby” is also built on a quaint, sweetly outdated notion that presidents possess some inherent greatness. As one character explains, Bobby teaches his brother compassion, and Jack teaches his brother strength. Both, the show suggests, are necessary for leadership, a view both heartbreakingly naďve and somehow reassuring in this day and age.
   “Jack & Bobby” has plenty of room to fail. If it shifts the balance too heavily toward the present time, it threatens to become just another teen drama. And if the glimpses of the future are kept as vague as they are in the premiere, they’ll come to seem like just a clever gimmick after all.
   But for now, those teasers—“He saw some dark hours during his presidency,” the former first lady recalls in 2049, “and it was those times he used to say, ‘the wrong brother became president’ ”—are reason to keep coming back.
   After all, a WB drama that offers a credible view of what the world will be like when its core audience is all grown up is an impressive experiment for the network—and one that deserves your vote.