People in all 50 U.S. states are voting in elections on Tuesday that will determine which party controls Congress for the next two years.
The vote has been going smoothly, although a few areas reported problems with electronic polling equipment.
The problems forced officials to extend voting hours in at least two counties, one in the midwestern state of Indiana, the other in the eastern state of Pennsylvania.
National pre-election surveys indicated that the war in Iraq was uppermost in voters minds as they headed to the polls, and significant support for opposition Democrats who hope to regain control of the House of Representatives for the first time in 12 years.
But the surveys also indicated that several key races were closer than they were earlier, and Republican leaders are claiming they have the momentum in the election.
Tuesday's elections also include voting for governors in 36 states, along with ballot questions on issues ranging from abortion and homosexual marriage to stem cell research.
President Bush and First Lady Laura Bush voted in their hometown of Crawford, Texas early today and later returned to Washington.
Republicans currently hold a majority in both the House of Representatives and the Senate.
Both parties were concentrating their efforts on getting their supporters to the polls.
On Monday, the president campaigned in the southern states of Florida, Arkansas and Texas. Mr. Bush urged all to vote Republican if they value their own security and if they want low taxes. Although the president is not running for office, he has campaigned on behalf of Republican candidates.
Democrats have appealed to voters to force a change in Washington.
Members of the House of Representatives serve two year terms and are all elected at the same time. Senators serve six year terms, with one-third of the 100 seats contested every two years.
Information for this report is provided by AP, AFP and CNN.