PRESIDENT TRUMP has so far failed to supply a credible remedy to the economic ills that prompted so many of his followers to cast a ballot for him in 2016. Of course, many of Mr. Trump’s voters were expressing not only support for him but disenchantment with the Democratic alternative. Democrats have responded to this devastating defeat mostly by preaching “resistance” to Mr. Trump and the Republican majority on Capitol Hill. However, if they are to recover politically and — more important for the nation’s overall political health — turn our political tribal warfare into something more like a battle of ideas, the Democrats must declare what they are for.

In that sense, we give them credit for Monday’s rollout of a new message aimed at the struggling middle class; they have decided to start trying to articulate a new vision. The question is whether their “A Better Deal” offers an alternative to Trumpism that is both clear and well-calculated to cure what really ails the American economy.

We don’t envy the Democrats’ task: In many ways the U.S. economy is performing well, operating at nearly full employment and growing at a steady if modest pace. Its problems are not spectacular but structural: lagging productivity growth, subpar labor force participation, slow wage growth, income inequality. Over the horizon, even more potentially job-killing automation looms. No one has foolproof answers for these complex challenges, which affect not only the United States but also developed economies around the world.

Even allowing for the degree of difficulty, however, the Democratic response, as sketched so far, is less than compelling: Its declared premise, that the economy is “rigged” against middle-class people, has a basis in the reality of Washington special-interest politics but seems better calculated to placate the party’s ascendant left wing than to start a serious policy conversation. American capitalism needs reform, not delegitimization. The Democrats offer one interesting idea in this respect — beefed up antitrust efforts to help bring down prices of airline tickets and the like. Otherwise, they rehash ideas that Mr. Trump himself has embraced at least rhetorically (massive new infrastructure spending; tougher negotiations between Medicare and the pharmaceutical companies) or play small ball (a tax credit for business to do job training).

The Democratic message includes nothing, yet, on trade, a major omission, given Mr. Trump’s effective exploitation of the issue. Yet perhaps it was better to remain silent than to admit the contradiction between House Minority Leader Nancy Pelosi’s (Calif.) promise that Democrats would confront “rising everyday costs” and the higher consumer prices that would result from the protectionism favored by both Mr. Trump and the Democratic left. Democrats also had nothing to say about tax reform, possibly because the clearest need is for a more internationally competitive (i.e., lower) corporate rate, which is what President Barack Obama correctly concluded, but populists abhor. Democrats are right that the United States hungers for a more equitable and effective alternative to GOP economics; obviously, though, they’re still working on it.