THE OUTCOME will shape coming political battles, including how to stimulate the economy and manage Social Security.
If Republicans keep their House edge and pick up just one or two Senate seats, they would control all three branches of government. Democrats, for their part, could present President Bush with a united opposition if they hold onto the Senate and add seven House seats.
The prospect of more of the same - Republicans holding the House, Democrats commanding the Senate and Bush navigating between the two - was also very much a possibility.
At stake Tuesday: all 435 House seats, several dozen of which were hotly competitive; 34 Senate seats, of which six to eight looked like tossups; and 36 governorships.
Voters also were choosing state legislatures, now split almost evenly between the parties, and deciding more than 200 ballot initiatives in 40 states.
For political analysts, the evening promised to be a chore - Voter News Service said late Tuesday afternoon that it would not be able to provide results of state and national exit poll surveys of voter attitudes, valuable data that election-watchers use to explain voting patters and predict trends.
In the weeks heading up to Election Day, VNS - a consortium of ABC, CBS, NBC, CNN, Fox and The Associated Press - was never able to work out the bugs in the part of the exit poll used to glean detailed information on how people feel about issues and how certain groups voted. The consortium rebuilt its system in response to the 2000 election, when television networks twice used its information to make wrong calls in the decisive Florida vote.
VNS also counts actual votes, and that operation was not affected, it said.
The president himself did not want to raise expectations for his party.
After voting Tuesday at the fire station near his ranch in Crawford, Texas, Bush seemed to signal that the day could go either way, first flashing a thumbs-up and then turning his thumb to the side when asked about Republican chances.
"I'm encouraging all people across this country to vote," he said before driving off to get ready to return to the White House.
Federal observers were dispatched by the hundreds to polling places in 14 states in the most ambitious monitoring of the nation's ballot boxes since 1960s civil rights efforts.
Ã¢ÂÂ¢ Learn how voting technologies work As for the process of voting, all eyes were on Florida. With memories still fresh of the 2000 Florida balloting fiasco and more than 200 counties trying new voting equipment, the suspense was not just over winners and losers but whether counters would be able to tell the difference.