Most impeachments have not been against presidents, but rather judges, cabinet officers, senators. These impeachments seem to take about as long as presidential impeachment do, and offer no support to the myth of long impeachments. In addition, much other business has been accomplished at the same time as these impeachments.
On July 3, 1797, evidence of an offense by Senator William Blount became known. Four days later, the House impeached him and the next day the Senate expelled him.
Evidence of an offense by Judge John Pickering became known on February 4, 1803, and the House voted to impeach him on March 2, 1803. The Senate didn't try him for another year, but spent 9 days on it when it did so.
Supreme Court justice Samuel Chase was impeached in late 1804 (I don't know how long the impeachment took) and 30 days later he was tried in the Senate, which completed the trial on March 1, 1805.
Judge James Peck was impeached on April 24, 1830, a month after the Judiciary Committee recommended it. The Senate took up the trial the following January and spent three days on it.
Judge West H. Humphreys was impeached on May 19, 1862. The Senate tried and convicted him in one day on June 26, 1862.
Secretary of War William W. Belknap was impeached on March 2, 1876, and the Senate trial was completed on August 1, 1876.
Judge Charles Swayne was impeached on December 14, 1904, and his trial was over on February 27, 1905.
Judge Robert W. Archbald was impeached on July 13, 1912, and the Senate trial was over on January 13, 1913.
Judge Harold Louderback resigned before his impeachment went to trial.
Judge Halsted L. Ritter was impeached on March 2, 1936, and the 11-day Senate trial ended on April 17th of the same year.
Judge Harry E. Claiborne was impeached on July 22, 1986, and the trial ended on October 9, 1986.
Then Judge and now Congressman Alcee L. Hastings, was impeached on August 3, 1988, and the Senate trial was over on October 20, 1988.
Judge Walter L. Nixon was impeached on May 10, 1989, and the Senate trial was completed on November 3, 1989.
Conyers goes on:
The final plea was: "Why not try? What do you have to lose?" Impeachments, however, both successful and unsuccessful, have precedential consequences – they set standards for future presidential behavior. The House Judiciary Committee's rejection of an article of impeachment against President Nixon for failing to file tax returns, for example, was used as precedent in acquitting President Clinton for impeachment based on personal misdeeds.
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