Richard M. Nixon was never impeached. After being assured he would be found guilty in a US Senate impeachment trial, he resigned before that happened on 9August 1974.
The role that the senate has in the impeachment process is sole power to try-to judge, sit as a court-in impeachment cases.
Johnson ignored the Tenure of Office Act.
Under current Senate rules, the Chief Justice of the US Supreme Court presides over any impeachment trials.
court
the judicial branch
The vice-president of the US normally presides over the senate, including impeachment trials. In the special case that the president is impeached, the Chief Justice of the US presides over the trial.
Not every impeachment is put on trial.
The Trail of Tears ended in the early 1840s.
In the Senate. The link below has a picture of the Senate at the impeachment trial of President Clinton (you can also see that the Senate is being presided over by Chief Justice Rehnquist--he is easy to recognize because of the stripes on his black judicial robe).
The Cherokee Trail of Tears ended in North West Oklahoma.
Trail Motorsport ended in 2009.
Andrew Jackson was not impeached; Andrew Johnson was. When the Radical Republicans were in charge of Congress, they hoped that the South was punished severely, and Johnson talked tough about Reconstruction. Andrew Johnson then proceeded to do exactly opposite of what he had promised, vetoing every act that helped the new freedmen and allowing a swift and extremely lenient reunion for the Southern states. The Radical Republicans were astonished and tried to kick him from the position of President.