Serious efforts were launched to impeach President John Tyler in 1843 and President Herbert Hoover in 1932, but were rejected by votes of the House. President Richard Nixon resigned in 1974 after the House Judiciary Committee voted out three impeachment charges against him. Only one president has gone through the full process. The Senate trial took 12 weeks, and ended with senators voting 35-19 to impeach him. But that was one vote shy of the necessary two-thirds vote, and so Johnson was acquitted.
Presidents are deathly afraid of the process.
John Kennedy told his Cabinet colleagues that it was the fear of impeachment that prompted him to take a strong stand against the Russians in the 1962 Cuban missile crisis. Former Attorney General Edwin Meese said the discovery of the Iran-Contra arms deals in November 1986 sparked alarm that President Ronald Reagan might have to stand impeachment for violating the Boland amendment that forbade the administration from assisting Nicaragua's Contra guerrillas. The work is done by the House Judiciary Committee, which holds hearings to gather testimony, combs through any other evidence, and decides what is impeachable. It doesn't have to follow what the law books say, and in history often hasn't. The House Judiciary Committee voted to impeach President Nixon in 1974 on general charges of abuse of presidential powers, which is not a federal crime.