The Senate’s First Impeachment Trial
Tennessee Senator William Blount was the first person impeached by the House of Representatives. The House voted to impeach Blount - a delegate to the Federal Convention of 1787 and signer of the Constitution - in 1797 based on his participation in a conspiracy to help Great Britain take over the Spanish-controlled territories of Louisiana and Florida.
The Senate voted to expel Blount shortly after the House impeached him. In the subsequent trial, senators debated whether members of Congress could be impeached (and convicted) either during or after their term in office.
The Senate voted to dismiss the articles of impeachment against Blount after concluding that it lacked jurisdiction to convict him. The Blount trial set two important precedents. It signaled that senators believed that they could not convict impeached officials if they are not in office at the time of the trial. It also established that members of Congress are not subject to impeachment and conviction.
More information on the trial can be found here.