Clinton's and Dubya's problems -- romantic and terroristic -- are trivial compared with President John Ballentine's. At least Monica and Osama were identifiable outsiders. The national and sexual security of President Ballentine, on the other hand, is threatened from within: Someone in his own Secret Service seems to be cuckolding as well as planning to assassinate him.

Kiefer Sutherland, left, Michael Douglas and Eva Longoria are agents at odds in "The Sentinel." "The Sentinel" Rating: PG-13 for violence and some sensuality. Starring: Michael Douglas, Kiefer Sutherland, Eva Longoria, Kim Basinger. Director: Clark Johnson. "The Sentinel" Web site Post-Gazette Family Film Guide review of 'The Sentinel'

No traitor has besmirched the ranks of presidential bodyguards in its 141-year history, but there's a first time for everything. That's the intriguing idea behind "The Sentinel," a political-action thriller based on retired Secret Service agent Gerald Petievich's novel.

The premise has promise. Heroic veteran Pete Garrison (Michael Douglas), who once took a bullet for a commander in chief, is one of a trio of agents charged with finding and foiling the mole. Heading the team is chief investigator Dave Breckinridge (Kiefer Sutherland), Garrison's protege turned enemy, still nursing a nasty grudge against his former mentor for personal reasons -- cherchez la femme.

Look for a woman, too, as the third member of our S.S. investigative team: Foxy rookie agent Eva Longoria, aka Gabrielle from "Desperate Housewives." Look for Desperate First Ladies in the form of Kim Basinger as the president's (overtly Stepford but covertly libidinous) wife, Sarah.

First mandated step for the agents is a polygraph test of loyalty, which Douglas flunks. When his colleagues show up to gently arrest him, he does what any innocent Secret Service man in his position would do -- escapes out the back door and goes on the lam, to vindicate himself and solve the case on his own.Sutherland and the rest of world, oddly enough, view his flight as more a sign of guilt than innocence. Thenceforth, the film is occupied with the chase-race against assassination time and the anticipation of each other's high-tech tricks.

In yet another "flawed but sympathetic" hero role, Douglas is competent. Always-attitudinal Sutherland and dignified Longoria avoid the cliched pitfalls of their roles, while Basinger and David Rasche give good, deliberately cliched renderings of a bland-leading-the-bland First Couple.

Director Clark Johnson directs the fast-paced traffic excitingly, until George Nolfi's screenplay (or perhaps Petievich's book) runs out of intelligent insider-situational dialogue and turns to implausible supplements for suspense. My notes (when subpoenaed by the Supreme Court) will show that the initial action and suspense are top-notch. But don't ask too many probing questions about the death plot's rationale, once it is finally unraveled.

And certainly don't ask why Sutherland keeps chasing (and Douglas keeps escaping) without backup support to speak of. The two top Secret Service aces in a one-on-one match, with the president dodging bullets in a dark stairwell? It's like Don Rumsfeld personally chasing Dick Cheney through the Pentagon after hours. Much action. Much huffing and puffing. Not a pretty thing.