Final answer:
The Radical Republicans attempted to remove President Andrew Johnson through impeachment, which is a two-step process where the House can impeach with a simple majority and the Senate then decides on removal with a two-thirds majority. Johnson was impeached but acquitted by one vote and remained in office.
Step-by-step explanation:
The Radical Republicans attempted to remove President Andrew Johnson from office through the process of impeachment. Impeachment involves formally charging a public official with serious wrongdoing, and it is a two-step process defined by the Constitution involving both chambers of Congress. Initially, the House of Representatives can impeach a president with a simple majority vote for 'high crimes and misdemeanors'. If impeached, the next step is for the Senate to potentially remove the president from office, which requires a two-thirds majority vote with the Chief Justice of the Supreme Court presiding over the trial.
In the case of Andrew Johnson, the House successfully impeached him by accusing him of encroaching on the powers of Congress, particularly for violating the Tenure of Office Act. However, during his Senate trial, Johnson was acquitted by just one vote, subsequently failing to meet the two-thirds majority needed for his removal. Thus, although he was impeached, Johnson continued to serve as president.