To anyone watching the oil spew into the Gulf of Mexico, the argument for curbing this country’s appetite for fossil fuels could not be clearer. President Obama was right last week when he called on America to unify behind a “national mission” to find alternative energy sources, sharply reduce its dependence on oil and cut its greenhouse gas emissions.

We were disappointed, however, that Mr. Obama’s address failed to insist that the best way to do all of these things is to establish a broadly based, economywide cap-and-trade system that would put a price on carbon emissions. He opened the door far too wide to alternative policies that aren’t real alternatives  and to more stalling.

A House bill approved last year would set up such a system. Action in the Senate has been delayed for months, as Republicans, and some Democrats, have argued without any real proof that capping and pricing carbon emissions would cripple the economy by driving up the cost of energy.

On Wednesday, Democratic leaders, who have promised to bring an energy bill to the Senate floor after the Fourth of July recess but are nowhere near agreement on what should be in it, will troop down to the White House. This time, Mr. Obama must stress, explicitly and emphatically, that a conventional energy bill will not do  and that attaching real costs to older, dirtier fuels now dumped free of charge into the atmosphere is the surest way to persuade American industry to develop cleaner fuels.