WASHINGTON, Nov. 5 (Xinhua) -- On Tuesday the United States is set to hold its midterm elections, which will have profound impact on U.S. politics for the next two years.

According to U.S. law, elections for U.S. lawmakers take place every two years, either concurrently with or two years after each presidential election. Because the latter take place between two presidential elections, they are known as "midterm elections."

During every midterm election, all members of the House of Representatives, the Congress' lower chamber, are up for reelection, as are one third of Senators, who fill the upper chamber.

For this year's midterm elections, 35 of the Senate's 100 seats are contested, 33 of which through regular election and two are through special election, meaning the seat is vacated by the previous senator before their terms were scheduled to end.

Of the 35 Senate seats up for election, 24 are currently held by the Democratic Party, two are by independent politicians who caucus with the Democratic Party, and nine are by the Republican Party.

This put the Democratic Party at a disadvantage to win the Senate majority through this year's midterm elections, as they have to defend significantly more seats than the Republicans do.

In the U.S. House of Representatives, all 435 seats, allocated to each state based on their population, will be up for election. The Republican party now holds 235 seats, as opposed to the 193 seats held by the Democratic Party. There are seven seats currently vacant due to resignations or other reasons.

The U.S. Congress is the legislative branch of the U.S. government. Both the Senate and the House of Representatives have the power to draft and pass laws. The Senate also has the power to approve some senior government officials based on the president's nomination, while the House of Representatives has the power to initiate impeachment processes.

If the Republican party manages to hold on to the majority in both chambers, it will bolster the current administration's legislative agenda, if the Democratic Party wins the majority in either the House or the Senate, it can greatly undermine the current administration's policy efforts in the next two years.

Aside from members of Congress, this year's midterm election will also produce 36 state and three territorial governors, mayors of important U.S. cities such as Washington D.C., San Francisco and Phoenix, as well as lawmakers making up 87 of 99 state legislature chambers across the country.

Historically, midterm election results are usually against the favor of the president's party. Since the U.S. civil war, the president's party on average lose 32 House seats and two Senate seats during midterm elections.

Midterm elections are usually set on the first Tuesday of November. Voting times vary by state, with voting centers opening as early as six in the morning and closing as late as nine in the evening. The final result is usually yielded early next day, but sometimes due to small difference margins in certain races, the official result can take longer to confirm.