If Mr. Obama wins re-election, he could simply refuse to sign any budget-busting tax cut for the rich — who, after all, have received much larger pretax raises than any other income group in recent years and have also had their tax rates fall more. Republicans, for their part, could again refuse to pass any partial extension.

And just like that, on Jan. 1, 2013, the Clinton-era tax rates would return.

This change, by itself, would solve about 75 percent of the deficit problem over the next five years. The rest could come from spending cuts, both for social programs and the military.

Over the longer term — 20 years — letting all of the Bush cuts lapse would close only about 40 percent of the budget gap. But 40 percent is a great start. No one is seriously suggesting that all deficit reduction should come from higher taxes. Much of it will have to come from slowing the growth rate of medical spending, which is the main cause of the long-term deficit.