IN HIS remarks on vetoing the Republican tax cut bill, the president should have quit while he was ahead. He was right to cast the veto, and he did a good job of explaining the multiple reasons why the showy bill deserved to be struck down. But lest anyone think -- correctly -- that deflecting the tax bill was his major objective this year, that it represented the heart if not the entirety of his agenda, he then went on.

"In the face of my determination," he said, the congressional Republicans ought not "throw in the towel," meaning just pass the appropriations bills and go home. "That would be a disservice to the American people." He invited his adversaries instead to join him in bipartisan efforts to "save" Social Security and Medicare. That's how he started the year, of course. Both of the giant programs for the elderly are in trouble. When the baby boomers retire, neither will have enough money to cover its costs. The president earlier in the year, and again yesterday, invoked their plight to ward off the tax bill. Save Social Security -- and Medicare -- first, he rightly said.

But the problem is that he no more than the Republicans has a serious plan to do so. Rather than give a tax cut, he would pay down debt in the name of these programs. It's a sensible thing to do; among much else, it will make it easier for the government to borrow again when the boomers retire and costs begin to soar. But that doesn't solve the structural problems -- the fundamental mismatch between likely revenue and costs -- so much as it defers the days of reckoning. Benefits still must be cut or additional sources of revenue found. The president has studiously avoided making any such proposals for Social Security. For Medicare, he has proposed some marginal cost containment, but also a huge add-on in the form of a popular and ultimately necessary prescription drug benefit that would significantly increase costs.

The Republicans have spent the year pretending to be prepared to make deep domestic spending cuts for which they lack the votes and which would do real harm. The president has rightly called them on it. But he has likewise spent the year pretending to be ready to reform Social Security and Medicare even while skirting the necessary steps. The veto keeps the long-term fiscal prospect from becoming worse. That's as far as the president has yet gone.