Only the U.S. House of Representatives can impeach a sitting U.S. President, and it must do so with a simple majority vote on one or more articles of impeachment. Any member of the House of Representatives can introduce an impeachment resolution, or the House as a whole can initiate the impeachment process by passing a resolution.
Once an impeachment resolution is introduced, the chairman of the House Judiciary Committee calls for the full committee to investigate the charges against the president. The Judiciary Committee can decide that the charges against the president are unwarranted, or it can move forward with the process by introducing an Articles of Impeachment resolution to the full House of Representatives. The members of the House vote on each of the articles of impeachment, and if any of the articles are approved by a simple majority, the president is impeached.
When the House of Representatives impeaches a U.S. President, he is not automatically removed from office, or barred from running for other offices in the future. After the House of Representatives passes a resolution impeaching the president, the U.S. Senate holds a trial to determine if the president is guilty of the charges against him. Two-thirds of the members of the Senate must return a guilty verdict in order to convict the president. The Senate holds separate votes to decide on removing the president from office and barring him from holding offices in the future.