At stake are all 435 seats in the House of Representatives, 34 seats in the Senate and 36 state governorships. There also are local initiatives in many of the 50 states.
People went out to vote in weather that included snowy skies in the northern state of) Wisconsin, a chill in (southern) Texas, and rain in (eastern) North Carolina to make their choices.
President Bush voted in his home state of Texas and later returned to Washington, D-C, to await returns from the election, which comes midway through his four-year term. The president spent the last few days campaigning for Republican Party candidates, including his brother, Jeb, who is in a tight race to retain the governor's post in the southern state of Florida.
On the national level, both Republicans and Democrats have a chance of taking complete control of Congress. When the Senate reconvenes later this month each party will have 49 Senate seats, with two independents, while in the House of Representatives Republicans have a six-seat advantage.
Public opinion polls indicate that control of the U-S legislature could hinge on a few critical races.
Historically, the party that controls the White House loses congressional seats in mid-term elections. But White House officials say they are optimistic that President Bush's popularity will help them break that trend and add seats.