Ah, impeaching a US President, the noblest of all the US Congress sports. And here is how it happens.
In the USA, an impeachment is 'a formal accusation of a crime and/or improper conduct against a US official'. If someone is tried and convicted they will be removed from their present office and may be prevented from holding any future office.
The US Constitution says that a President can be impeached for 'high crimes and misdemeanours'. There is no specific definition of what this means, although something like lying to Congress is covered by this term. If the House of Representatives considers the President to have committed a 'high crime or misdemeanour' they will hold a majority vote on whether to impeach and then the trial will take place in the US Senate.
An impeachment trial takes place in the Senate Chamber, with the entire Senate sitting as a 'Court of Impeachment'. The Chief Justice of the Supreme Court presides, seated in the presiding officer's chair on the Senate rostrum. All the Senators must be seated at their assigned desks on the Senate floor. The tables in front of the rostrum are used by the President's lawyers on one side and by the Members of the House of Representatives presenting the prosecution's case on the other (the Managers). Managers must have voted for impeachment in the House of Representatives and be willing to argue the House case against the impeached President1. For an impeachment trial to be successful, two-thirds of the Senate must vote for a conviction at the end of the trial2. Once a conviction is secured, the President would immediately be removed from office and a majority vote may be taken by the Senate to prevent that President from holding any future public office.
A Step-by-step Guide to the Proceedings
After the House have decided to impeach the President and Managers have been appointed, they send a message to the Senate notifying it that Managers for an impeachment have been appointed and await to deliver Articles of Impeachment (ie what the defendant has done to deserve impeachment). The Senate responds by notifying the House of the day and time it wishes to receive the Managers.
The House Managers carry the Article(s) of Impeachment to the Senate chamber on the designated day and, after their presentation, a House Manager or Senate Officer reads the Articles to the Senate.
The day after the Articles' presentation, the Senate's formal preparations for trial commence at 1pm, the Chief Justice of the Supreme Court is summoned to preside and is sworn in by the Presiding Officer of the Senate. Then all Senators are sworn in as jurors by the Presiding Officer.
A Writ of Summons is delivered to the impeached President by the Sergeant-at-Arms, saying what time and day the trail is due to begin and summoning them to appear. The President may appear in person, or may choose to allow lawyers to represent them.
On the designated day, usually at 12 noon, the trial commences. During the trial, no legislative business takes place unless unanimous consent is given by the Senators.
The trial is open to the public and press, unless the Senate votes to close all or part of it.
Any witnesses are subject to examination and cross-examination by the Managers and defence lawyers. Senators wishing to question a witness submit their questions in writing and these are read aloud by the Presiding Officer or by a Senate clerk.
Any opening motions are limited to one hour per side, as are any subsequent questions or motions. Opening and closing statements of both sides are without time limitation, unless unanimous consent is given to set a time limit.
The entire Senate then goes into closed session to deliberate as a jury over the arguments heard.
When the Senate returns to open session, they commence voting. Each Article of Impeachment is put to the Senators and voted upon separately. Senators vote by responding to their name when called out loud, standing at their desk and answering 'guilty' or 'not guilty'.
If any Article of Impeachment receives a two-thirds vote of 'guilty', the President is considered impeached and removed from office.
After all the Articles have been voted on, the Senate renders judgment, pronouncing conviction; or it may choose, by majority vote, to 'disqualify' the President from holding any public office in the future. If the President is removed from office, they become a private citizen and, therefore, may face public or private prosecutions for their impeached actions.
Isn't This a Bit Heavy Handed?
Depends how seriously you regard the Senate. However, if the Senate did think it too much, they can condemn or reprimand the President, which they did to President Jackson in 1834, although it's not nearly as much fun as a trial and censure isn't really taken as seriously by a President as by a Senator. Jackson's censure was even revoked three years later by a different Congress.
Actually, the above procedure for impeaching is the same when impeaching anybody who works for the federal US Government, such as judges, Senators, etc. Also, individual States can impeach and convict their own officials in their Congressional Houses3.