Film studies: She's classy. She's presidential. She's Reese

The unlikely names run together in chattery abandon - Parker Posey, Heather Graham, Charlize Theron, Angelina Jolie, Cameron Diaz, Alicia Silverstone, Drew Barrymore, Liv Tyler, Neve Campbell, Denise Richards, and so on. Los Angeles, crowded out with drop-dead kids, seems to require some Warholian likelihood that every one will get her chance in a picture. It's a sort of snapshot souvenir - proof that they were here. What's the risk, the system asks: you get new meat on the screen, a 10 for ravishing desirability, and the girl walks off with a few hundred grand and the experience. It's a start in life. Where's the harm, when the kids are wide-eyed know-nothings with this one loony sophistication - they seem to possess every acting pose gathered in a century of movies.

So long as none of them thinks she's Reese Witherspoon. Ms Witherspoon is still only 23. She attended Stanford University after coming out of Nashville, Tennessee - and that, along with her fancy tweed-and-brogues name, is enough to indicate some ripe old southern family, acquainted with money and class, with a dash of eccentricity. You don't send a pretty girl out into the wilds of America calling her "Reese Witherspoon" without a large degree of ignorance, or a tease's urge to watch what happens. Equally, if you're going to grow up as "Reese Witherspoon", you need a certain mix of nerve.

Reese Witherspoon burst upon the scene three years ago with a film called Freeway in which her character, Vanessa Julia Lutz, became one of the most commanding Wanted (and Dreaded) posters of modern film. Freeway opens with a classic demolition of the high-school myth. It's up to us whether we see it as satire or flat record, but there's a senior class - strapping young animals - struggling to read the blackboard sentence "The cat drinks milk". Vanessa is comprehensively made up, dressed for action, and either she's a natural gallows comedian or it really takes her 30 seconds to struggle with the sentence. But when she gets it right, she turns for her reward: a lingering, open-mouth kiss from her boyfriend, "Chopper".

Later on, it is said that Vanessa is illiterate and depraved, though she does seem to read a few fragments for plot information. It's more to the point that Vanessa is inclined to take shelter in dumbness. It's vital that she is also very acute and knows that America measures success by survival and getting your story in print first. She's white trash, equipped with a tuneable Texas whine, and the ambivalent seductiveness of a Lolita with killer bees in her underpants. She's also a God-fearing innocent who, when life sends her on the road, falls in with no less than "the I-5 highway serial killer", the horrid Bob (brilliantly played by Kiefer Sutherland). But she gets the drop on him and then plugs a few bullets into him when she's made sure he's on terms with the Lord Jesus Christ his Saviour.

Directed by a first-timer, Matthew Bright, Freeway is a blithe inversion of threatened-youth pictures. This kid is a lethal mix of raw energy and TV dialogue. She "wins through" in the end, gets her due as the slayer of evil Bob and deserves an hour on Oprah as the ideal American waif who stood up to cruel fate. Freeway goes helter-skelter fast, and you don't want it to stop. Let's just say that the film was co-produced by Oliver Stone, yet is subtler and more alarming than his own Natural Born Killers. And it depends absolutely on Reese Witherspoon.

In her new picture, Election (directed by Alexander Payne), she is something like the young, hard bud of a Hillary Clinton in the making. Tracy Flick is a high-school princess, an A student, a sure thing for class president. But her ghastly primness irritates an idealistic young teacher (Matthew Broderick) and persuades him to sabotage her campaign. (He is also prompted by the fact that she has had an affair with another teacher that ruins the guy's career.) Where Vanessa was a great lipstick smear across the screen, Tracy is buttoned up and repressed. (It's very intriguing that in the early affair the older man is amazed at her lubricity.)

There's a hidden force in Tracy, a neurosis, that comes out when she's thwarted. When her plan for putting up her own posters hits a small, fussy mistake, she turns into a witch, ripping out every poster in the school. Guess who wins the election? Guess what American city Tracy Flick is headed for? Election is, among other things, a poke in the eye for an America that has reduced itself to popularity contests in the name of democracy.

Reese Witherspoon has done other things - Cruel Intentions, Pleasantville, Fear, The Man in the Moon. Soon she will face a great test when she grows too old to play high-school Medusas. Is there an older woman waiting? We'll see, but in the meantime Reese Witherspoon is the best comic actress on the American screen. And her special brand of drop-dead is: that's what could happen to you if you stare too hard at her.

Election (15) is released on 24 Sept