WASHINGTON - The election of a Republican U.S. senator from Massachusetts on Tuesday to replace the late Edward Kennedy, a Democrat, puts U.S. President Barack Obama's ambitious agenda at increased risk.
On matters from healthcare to judicial nominees, Obama will no longer be able to prevail in the Senate with just the support of 58 fellow Democrats and the two independents who typically vote with them. The president will now need at least one Republican vote -- and that could be difficult.
Following are some questions and answers about the race, which saw Scott Brown become the first Republican since 1972 to be elected to the Senate from Massachusetts:
WHAT WILL BE THE FALLOUT?
Once Brown is seated, Democrats will lose their 60-vote Senate supermajority, which now lets them clear Republican procedural roadblocks and pass legislation -- or confirm presidential nominees -- without a single Republican vote.
It has often been difficult, however, to get members of the Senate Democratic caucus to stick together. They include liberals, moderates and conservatives.
The election of Brown gives Obama a bigger challenge. He will need the support of the entire Senate Democratic caucus as well as at least one Republican to clear procedural roadblocks. Republicans have opposed most of Obama's agenda, including his bid to revamp the U.S. healthcare system.
WILL OBAMA DEMOCRATS BECOME MORE INDEPENDENT MINDED?
Democrats in Congress may see Democrat Martha Coakley's defeat as a reason to break away from Obama's legislative agenda, including healthcare, climate change and financial regulation.
That, in turn, could result in Obama facing more resistance from Democrats as well as Republicans on Capitol Hill this year.
To be sure, Massachusetts voters voiced unhappiness with incumbents of both parties. Polls show the economy and jobs to be their top priorities -- not healthcare, climate change or financial regulation.
WHEN WILL BROWN BE SWORN IN?
Election officials have said it would take about two weeks to certify the winner, clearing the way for a Senate swearing-in. Republicans argue it should not take that long.
They note that Edward Kennedy was sworn in as a U.S. senator on November 7, 1962 -- a day after he won a special election to fill the seat once held by his brother President John F. Kennedy.
Senate Democratic leader Harry Reid said after Brown's victory on Tuesday night that Brown would be seated as soon as his paperwork is received.
WILL DEMOCRATS STILL CONTROL THE SENATE?
Yes. They will continue to decide what comes up for Senate votes and will still chair Senate committees.
COULD DEMOCRATS PASS BILLS WITHOUT A 60TH SENATE VOTE?
Yes. Before getting the Democrats' 60th vote, Obama won passage last year of major legislation to expand a federal children's health insurance program and a $787 billion economic stimulus. He did so with needed Republican support.
HOW LONG HAVE DEMOCRATS HAD A SUPERMAJORITY?
Democrats got their 60-vote supermajority last July when Minnesota Senator Al Franken was sworn in after a marathon court challenge of his 2008 win over Republican incumbent Norm Coleman. That was the first time either party had a 60-vote supermajority since 1979, when Democrats had 61.
With Kennedy's old Senate seat in Republican hands, Democrats will hold 59 votes, which will still give them one of the biggest Senate majorities in the last half century.
WHAT ARE THE POLITICAL RAMIFICATIONS?
The Republican victory is seen as a repudiation of Democrats' healthcare legislation, which was a major factor in the race.
Brown, just as Obama did in being elected president in 2008, tapped into voter anger about Washington gridlock and the ailing U.S. economy, which features a double-digit jobless rate.
Even before the votes were counted, the special election in Massachusetts was seen as a wake-up call for Democrats.
They need to win back the support of many of their own constituents if they want to retain their seats in the November election when about a third of the 100-member Senate and entire 435-member House of Representatives will be up for grabs.
WHAT ARE THE OPTIONS FOR DEMOCRATS ON HEALTHCARE?
Democratic leaders are attempting to move the healthcare legislation through quickly, before Brown is seated as a member of the Senate.
Obama stepped up the pace of negotiations over the past week. Interim Democratic Massachusetts Senator Paul Kirk has vowed to back the healthcare bill while he remains in office.
Democrats could try to win at least one Republican Senate vote. Likely candidates would be Olympia Snowe and Susan Collins, both moderates. Support from either would likely entail potentially troublesome changes in the legislation.
WHAT OTHER MAJOR EFFORTS IN CONGRESS COULD BE AT RISK?
An already uphill battle to win passage of legislation to combat global warming will become tougher. Same with measures to tighten regulation of the U.S. financial industry.
(Additional reporting by Ros Krasny; Editing by Will Dunham and Peter Cooney)