The Democrats' last redoubt in Washington -- their minority outpost in the Senate -- became considerably shakier last Tuesday with the fall of their leader, Senator Tom Daschle of South Dakota, and the loss of a total of four seats. But it remains the party's best chance of exercising some form of political relevance in the second Bush administration, by using its minority power selectively to filibuster objectionable legislation and unacceptable presidential nominees, and by continuing to make alliances with the dwindling band of Republican moderates.

Whether or not President Bush intends to make good on his promise to reach out to Democrats in his second term, victorious Republicans are already shaping a fresh agenda in Congress. In the House, the Democrats' impotence can only deepen as their bare-knuckled nemesis, Tom DeLay, the majority leader, returns more powerful than ever after his gerrymander of Texas delivered the four-seat increase in the G.O.P. majority. If Mr. Bush plans to follow through on his sketchy talk of compromise, that would oblige him to rein in the runaway partisanship of Mr. DeLay.

With the Democrats clinging to 45 seats in the Senate, the party is turning to a new Senate leader, Harry Reid of Nevada, who is short on charisma and silver-tongued oratory but, perhaps more usefully, is a conservative with a reputation for steeliness and attention to detail and a knack for floor skirmishing. Mr. Reid, a boxer and Capitol corridor guard in his student years, will need that battler's wiliness to deal with the Republican agenda -- from Supreme Court appointees to tax-code overhaul.

Senate Democrats will have the obligation of nay-saying through the filibuster, but with 45 seats, the party is vulnerable to having a few conservatives picked off here and there to defeat that tactic. They will therefore have to seize the occasional chance for compromise as Senator Reid musters an opposition that includes their defeated standard-bearer, Senator John Kerry. Considering the rebuff from heartland voters, Senate Democrats like Dianne Feinstein of California find comfort in Senator Reid's roots, but not some of his positions, like his opposition to abortion. ''I like the fact that he is a Westerner, frankly,'' Senator Feinstein said.

Mr. Reid has built credit as a negotiator with moderates across the aisle, who now return more endangered than ever. The Democrats should look for alliances with those Republicans, like Olympia Snowe of Maine and John McCain of Arizona, who were fighting for pay-as-you-go budgeting and rational intelligence reform before the election and may now be joined by a few more true conservatives who never liked Mr. Bush's fiscal recklessness but held their fire during the campaign.

The Democrats may find only marginal hope in the caution from Senator Arlen Specter of Pennsylvania, a G.O.P. moderate who survived the conservatives' purge attempt, that the Senate remains unlikely to approve antiabortion ideologues for court nominations. Mr. Specter, whose comments immediately provoked an assault from the right on his claim to the chairmanship of the Senate Judiciary Committee, is already back-pedaling. His ability to hang on to the post will be an early sign of the price the Republican right wants for the election results, and Mr. Bush's willingness to pay it.

Moderation seems an endangered word amid Republicans' exultation, but it may be the most to be wished for as Senator Reid rallies Democrats from their Election Day drubbing.