Lakeview Terrace, Neil LaBute, 110 mins, 15<br>Trouble the Water, Tia Lessin, Carl Deal, 90 mins, 15

America may have elected its first black president, but here are two sharp reminders that the scars won't heal overnight

The incoming Obama presidency has already begun to rewrite the book on race in the United States, but centuries of damage won't be healed overnight. As a reminder, here comes – of all things – a disposable but provocative LA-set thriller.

One of Neil LaBute's projects as director but not writer, Lakeview Terrace is released just when American audiences will surely have little time for it. The US is in, as they say, a very positive place right now – and here's a story about an interracial couple menaced by a black cop. The perversity of its timing is one of the film's main attractions.

Lakeview Terrace is a belated example of the "home-invasion" thriller genre that thrived in the 1980s and '90s (The Hand that Rocks the Cradle, Single White Female, et al) in which regular bourgeois folks faced avenging furies in mundane domestic settings. In Lakeview Terrace, written by David Loughery and Howard Korder, the nemesis is a suburban neighbour, an African-American police officer played by Samuel L Jackson.

The setting is a manicured residential enclave in the Los Angeles hills, where well-heeled young Chris and Lisa Mattson (Patrick Wilson, Kerry Washington) move into a new home. He's white, she's black, a fact that raises the hackles of their neighbour Abel Turner (Jackson). A widowed disciplinarian father of two, he disapproves of racial mixing, and contrives to make things uncomfortable for the Mattsons. His nastier actions are routine genre malice, but at his most interesting, Abel makes the couple the brunt of his "satirical" humour, confronting these enlightened children of a new America with their own entrenched prejudices. Contemptuous of white people buying into black culture, he sneers at Chris's love of rap: "You can listen to that noise all night long – when you wake up in the morning, you'll still be white."

Abel's most polemically barbed moment comes when a despairing Chris pleads, "Can't we all just get along?", consciously or not echoing the words used by Rodney King on TV after his beating by police sparked riots in LA. "Are you playing the race card?" retorts Abel. His function as a satirist provocateur is to remind us that the legacy of racism doesn't easily go away: gleefully rubbing everyone up the wrong way at his neighbours' party, Abel is the phantom of bigotry at liberal America's banquet.

Ordinary in its glossy execution, Lakeview Terrace derives much of its energy from Samuel L Jackson, his sardonic bully displaying a finesse that he doesn't get to use in his broader roles. As for the blandness of Kerry Washington and Patrick Wilson (a poor man's Matthew McConaughey), it not only draws us closer to Abel's perspective than to theirs, but also displays LaBute's antipathy to the superficially virtuous.

Lakeview Terrace comes across as a pulp corrective to the institutional piety of the huggy, Oscar-winning Crash, in which wisdom is got and differences resolved. Here, the film overplaying its hand somewhat, domestic-level racial conflict is staged against a background of apocalypse, CGI bush fires that spread until the LA hills, and apparently all America beyond, are engulfed in an inferno: a permanent state of burn-baby-burn.

Lakeview Terrace will probably be big in cultural studies forums, but the issues it dramatises look academic compared to the injustice depicted in Trouble the Water, about New Orleans and the effects of Hurricane Katrina. On one level, Tia Lessin and Carl Deal's extraordinary film is one of those affirmative American documentaries about people beating hopeless odds: its central figure Kimberly Rivers Roberts, a young resident of the city's deprived Ninth Ward, lives to perform a triumphant rap about her endurance.

On another level, the film brings us remarkable coverage of the floods, in Roberts's own camcorder footage, filmed as the waters rose. Her shaky images contain the kind of moments you see in apocalypse thrillers that use fake video footage to heighten the reality effect: the wind rising, dogs getting restless, a doomed drunk weaving across the street. But it's all horribly real, as Roberts reminds us: seeing herself as a one-woman CNN, she announces as she shoots, "Reporting live – we'll be bringing y'all more footage very shortly." Then the waters lap at her upstairs windows. This is live coverage, from the belly of the beast.

The horror piles up, terrible in its intimacy: we hear an old woman's desperate emergency call ("I'm gonna drown in the attic"), and the operator flatly telling her not to expect police aid. This is where Trouble the Water necessarily becomes a very angry film. When we see biblical scenes of stranded multitudes, we know these are not victims only of nature but of government: President Bush refused to bring troops back from Iraq to help, and no public transport was provided for evacuation, leaving the city's predominantly African-American poor to fend for themselves. After the floods, the Robertses return to their doorstep to find an eviction notice and a set of false teeth. In a bitter juxtaposition, the camera travels through the devastated Ninth Ward, while a PR woman twitters about how the touristy French Quarter is still in prime condition.

The US government's abandonment of black New Orleans makes Kimberly Roberts feel "it's like we lost our citizenship". While her experience has a happy outcome, the film reminds you that hers is among 1,000 stories from the Crescent City. Lakeview Terrace plays tauntingly with ideas about race in America, but Trouble the Water shows how destructively those ideas affect millions: it reveals the depths of the scars in the American system and makes you gasp at the enormity of the task awaiting the Obama regime.