NOW THAT the Democrats control both the White House and both houses of Congress, the party will have to consider carefully how it is going to rule. There are already fears among its members that it will over-reach itself and be penalised heavily for doing so by voters in the 2010 congressional elections, writes Mark Hennessyin Washington
Despite their gains in the Senate, the party's majority is not filibuster-proof and the Democrats, if their pledge to "reach across the aisle" is to mean anything, are also likely to want woo moderate Republicans such as Maine's Susan Collins, once again elected in her increasingly Democrat-friendly state on a promise to work closely with Obama.
The prospect of such support, if only some of the time, would give Democrats the opportunity to punish senator Joe Lieberman, the party's vice-presidential candidates in 2004, who now sits as an independent. He backed John McCain's campaign, to the fury of Democratic party elders, not least in a speech to the Republican National Convention in which he extolled Obama as "a gifted and eloquent young man", but insisted "eloquence is no substitute for a record, not in these tough times".
Until now, with a single-seat majority in the Senate, the Democrats had refrained from completely severing links with him. After Tuesday they hold 57 seats and could yet add to the tally once the three outstanding seats are decided. The arithmetic could make irresistible the temptation to hit back at Lieberman, who holds the prestigious chair of the Senate Homeland Security and Governmental Affairs Committee and sits on other committees.
The Democrat numbers in the Senate are also slightly more left- wing than the outgoing group, which could pose problems in time for Obama as he seeks to carve out a middle ground. New Mexico's Tom Udall and his Colorado cousin Mark Udall, who, as members of the House of Representatives both voted against the Iraq war, the Patriot Act, and most of George Bush's economic plans, take over from dependable, if dull, Republicans.
North Carolina's Kay Hagan, who defeated outgoing senator Elizabeth Dole, the wife of 1996 presidential candidate Bob Dole, will join a Democratic bloc that has been showing an increasingly jaundiced eye on free-trade agreements.
Nevertheless, moderates have been added to the Democratic mix as well: New Hampshire's Jeanne Shaheen and Virginia's Mark Warner, who takes over from 30-year Senate veteran John Warner, no relation.
On social issues, the new Democratic senators are all pro-choice on abortion and back gay rights, although Obama may wish not to concentrate on such areas in light of Californian voters decision to overturn the court-ordered legalisation of gay marriage.
The final make-up of the Senate will also be shaped by whether Alaska's senator Ted Stevens, convicted on seven corruption charges in the days running up to the elections, wins, and whether he is allowed to sit.
Ahead by 3,000 votes over his Democratic opponent, with 70,000 left to be counted, Stevens has already been told by Democrat Senate Majority leader Harry Reid that convicted felons cannot take their seats. If so, he may be forced to stand down, leaving, intriguingly, Alaskan governor Sarah Palin with the job of nominating a temporary replacement - though her exercise of that power could be challenged in court. Some conservative Republicans argue she should take the job herself and then run to hold on to the seat when an election takes place up to 90 days after Stevens would have been forced to stand down.