WHILE the Democrats and Barack Obama won big yesterday, even coming close to a filibuster-proof majority in the Senate, Obama will find their options substantially constrained by reality.

Their handicap is the financial condition of the nation they’ll inherit. Think of a trustee or conservator of a bankrupt company.

Those who fear a radical Obama miss the point of the lack of maneuverability of the next president. Behind the mortgage crisis looms the credit-card crisis, the student-loan crisis and the car-loan crisis. Sweating this mess out of the system will take two years of zero growth or contraction.

We won’t have a Great Depression, for the government will irrigate our economy with money. But we’ll have stagnation, followed by inflation.

So Obama will take office with unlimited political power but highly circumscribed practical power. He can pass whatever legislation he wants, but will be unable to indulge his ideology.

The irony will be bitter for the Democrats. Finally able to rise above the political limits they’ve faced, they’ll encounter new limitations in the fundamental problems of the economy.

The Republican Party’s role is to rebuild in the shadow of the frustrations of the Obama presidency. Just as MoveOn.org built the massive grass-roots base that yesterday impelled the Democrats to victory, so Republicans must go down to their grass roots, get in touch with their base and rebuild an opportunity to win national elections.

Power has been bad for the GOP, sapping the party’s soul and eroding its purity. But opposition, especially when a socialist like Obama wrestles with the practical problems of capitalism, will be a heady experience for the Republicans. The conservative movement can be reborn in opposition in a way they never could have been as the governing party.

For political historians, it’s worth noting that Obama hasn’t scored the knockout that many predicted. As I write, it seems clear that John McCain will lose by a few points in the popular vote, not by the double digits so confidently predicted in the media polls. The fact is that most of the undecided voters went to the Republicans.

In the face of a mandate limited by reality and undermined by his inability to sweep the nation as had been predicted, Obama will face a difficult situation. As the economy falters, he’ll find himself unable to raise taxes as he wants and stymied in his plans for government takeover.

A very tough future, for a man who won such a heady victory.