USA — There 435 voting members of the U.S. House of Representatives representing the 50 states. All 435 seats are up for election every two years.

Republicans currently hold 237 of these seats. Democrats hold 193. There are seven vacant seats.

As of midnight on Election Day, Democrats were expected to win 203 seats, while Republicans were expected to win 194. Thirty-eight races were considered to be toss-ups, according to politics site and polling data aggregator Real Clear Politics.

For the Democrats, 173 of the seats were considered to be safe, 15 seats were likely go to the Democrats, and 15 were leaning toward the Democrats.

For the Republicans, 149 seats were considered safe, 20 were considered likely to be won by the GOP, and 25 were learning toward the Republicans.

Among the 38 races that were too close to call, Democrats currently hold five of these seats, while the Republicans hold 33. This means the Democrats have to defend far fewer seats than the Republicans.

A total of 218 seats are needed to gain a majority in the House of Representatives. According to statistical analysis site FiveThirtyEight, as of Nov. 1 the Democrats had an 85 percent chance of taking back the House.

States are divided into a certain number of districts based on their population size, in order to send a proportionate number of representatives to the House. Every state is guaranteed at least one seat, no matter how small its population.

In some states, the party in power will draw up district lines to give it an advantage in as many Congressional races as possible. This process is called gerrymandering.

According to the Washington Post, studies show this happens more often in states controlled by Republicans, though Democrats also engage in the practice.