1. Impeachment was established by the framers of the Constitution as a way to accuse a president of a crime and to hold a trial to determine if he or she is guilty of that crime.
2. The Constitution lays out two specific actions that could lead to impeachment and removal of a president from office -- treason and bribery.
3. A president can also be charged with and found guilty of "high crimes and misdemeanors," but the Constitution does not define what constitutes high crimes and misdemeanors, making impeachment on that basis more difficult.
4. It is not easy to get rid of a president, which is by design. Click here to read the steps in the process for impeaching a president.
5. To impeach a president, at least 218 of the 435 members of the House of Representatives must vote in favor of the articles of impeachment. There are 235 Democrats in the House.
6. If the House approves the resolution, the process moves to the Senate, where a trial is held.
7. It takes a two-thirds majority vote in the Senate (67 of 100 senators) for a president to be convicted of the charges brought in the article of impeachment. There are 45 Democrats and two Independents in the Senate.
8. Impeachment trials were held for President Andrew Johnson in 1868 and for President Bill Clinton in 1999, both of which ended in acquittals, meaning the presidents were impeached by the House but not convicted and removed from office by the Senate.
9. One vote kept Johnson from being convicted of firing the secretary of war, which went against a tenure act. And the Senate was 22 votes shy of convicting Clinton of perjury and obstruction of justice, stemming from a sexual harassment lawsuit filed against him by Paula Jones.
Click here for a detailed explanation of how impeachment works.
Click here for a list of House Democrats who have indicated they would support articles of impeachment.