SIX MONTHS ago, Vice President Al Gore seemed to have the Democratic primaries sewn up. On Wednesday, however, Bill Bradley formally launched a credible challenge to him. This raises the hope that, despite the obscene quantities of cash involved in presidential campaigns, competition remains possible. Whether that competition will yield a worthwhile contest of ideas is a question Mr. Bradley must now answer.

The Bradley campaign has done better than most people thought possible on three counts. It has amassed $12 million from donors impressed by the candidate's mixture of senatorial seriousness and basketball fame; this puts Mr. Bradley within striking distance of Mr. Gore, who has raised $18 million but already has spent a chunk of it. Second, it has assembled a competent staff, something that often eludes political campaigns. Third, Mr. Bradley is starting to do respectably in polls. Two recent surveys of New Hampshire voters suggest that Mr. Gore's lead has shrunk substantially, though nationally it remains formidable.

Crystal City, Mo., is Mr. Bradley's hometown, and his launch there hinted at the tone of his campaign. He will emphasize small-town values learned on the banks of the Mississippi; this will imply a contrast with Mr. Gore, who grew up in a posh hotel in Washington. He will present his rise from modest roots as a triumph of American social mobility, and so plant a second subliminal dagger between the vice presidential shoulder blades. But Mr. Bradley will have to offer more than this. Bob Dole's 1996 campaign proved that small-town origins and a heroic personal story are not enough to impress voters.

Hence the importance of the policy speeches that Mr. Bradley is promising. The candidate wants to speak for the people who remain poor amid America's prosperity. This is certainly a noble goal: One in five children live in poverty, while the soaring stock market has made kings of those who own bits of it. But Mr. Bradley has offered mixed signals on what he would do about this.

Mr. Bradley says he supports ethanol subsidies; but government payments to uncompetitive producers are a terrible way to help the disadvantaged. He has told a union audience that "if you want to help working families, you start with a union"; but because most poor Americans are not in union jobs, the role that unions play may actually be marginal. On the other hand, Mr. Bradley promises a plan to give all Americans access to health care; he says he will rein in the gun lobby; he talks feelingly about race; and he wants to mute money's voice in politics. Those themes sound promising; but they are only themes, not policies.