Impeachment has been generally reserved as a last resort of punishment for a sitting U.S. president who has demonstrated behavior rising to “high crimes and misdemeanors” while in office. There have been two presidents who have been formally impeached, another where impeachment was clearly imminent, and other cases where official complaints of malfeasance have been lodged, but no official congressional action taken.

John Tyler in 1842 was the first president to face a call for impeachment. In assuming the presidency after William Henry Harrison who died of pneumonia after serving just one month in office, Tyler was unpopular even among his own Whig Party (forerunner to the Republican Party). A Virginia congressman, John Botts, submitted a petition for Tyler’s impeachment in requesting an investigation of charges of misconduct based on the fact that it was believed Tyler was vetoing too many bills passed by Congress.

Things came to a head when Tyler vetoed a major tariff bill with Botts claiming that Tyler was abusing his power of the veto to “gratify personal and political resentment.” Botts’ call for impeachment was sent to the House Judiciary Committee who refused to hold hearings on the accusations.

In February 1868, something extraordinary happened in Congress. For the first time in history, the House of Representatives impeached a sitting president in Andrew Johnson. Johnson assumed the presidency after the assassination of Abraham Lincoln in April 1865. While Johnson, from Tennessee, was a staunch supporter of the Union Army during the Civil War, he was, to his heart, a Southerner. His roots were in the South.

“This is a country for White men,” he had frequently declared, “and as long as I live, it shall be a government for White men.”

Even as Lincoln’s running mate, Johnson never really won favor with the Radical Republicans, whose membership included men like Thaddeus Stevens and Benjamin Butler who wanted to guarantee the rights of the freedmen. One way to accomplish this was to pass the Reconstruction Laws that provided suffrage and civil rights standards to freed slaves, and also to prevent former Southern rebels from regaining control of their state governments.

In believing the Reconstruction Acts to be wrong and unconstitutional, Johnson repeatedly blocked their enforcement. He often gave pardons to ex-rebels. He hampered military commanders’ efforts to block the rise of Southern leaders to power. In frequent speeches and interviews, Johnson publicly expressed his defiance of the Radical Republicans.

The final blow came after the passage of the Tenure of Office Act in 1867. This law made it impossible for the president to dismiss important government officials without the permission of the Senate. In a move that infuriated the House, Johnson defied the act.

Johnson had long wanted to dismiss Secretary of War Edwin M. Stanton, who was the only member of Johnson’s cabinet who supported the Radical Republican agenda for Reconstruction.

Angered by Johnson’s open defiance, the House of Representatives formally impeached him in February 1868 by a vote of 126-47. They charged him with violation of the Tenure of Office Act, and bringing into “disgrace, ridicule, hatred, contempt, and reproach of Congress.”

It was left to the Senate to hold trial for Johnson, and in May of that year he escaped removal from office by just one vote.

In 1932, Pennsylvania Rep. Louis McFadden introduced two impeachment resolutions against President Herbert Hoover, largely based on the latter’s failure to adequately address the economic crisis that had beset the nation for the past 36 months. Both resolutions were eventually tabled by large margins and no impeachment inquiry nor proceedings would ensure.

President Richard Nixon was on course for a comfortable win in his 1972 reelection campaign. That was until June of that year when what was originally called by the White House as a “third-rate burglary,” five persons were caught prowling around the Democratic National Committee offices in the Watergate Hotel in Washington, D.C.

The five burglars, along with two men connected with the Nixon campaign, G. Gordon Liddy and E. Howard Hunt (two of the notorious “White House Plumbers”) appeared later before a Grand Jury.

Nixon took 60.7 percent of the vote that November, winning 49 states and 520 seats in the Electoral College, easily defeating rival Sen. George McGovern.

There has always been the question of whether Nixon had advance knowledge of the burglary, or whether he did not know what others were doing in his name. According to a taped conversation between Nixon and his Chief of Staff H.R. Haldeman, a furious president asked “who was the ahole who ordered it?”

The five burglars had received hundreds of thousands of dollars in “hush money” not to divulge who was the ring leader, while Nixon and his team tried to quell the damage.

Nixon would promise that there would be “no whitewashing at the White House,” but, behind the scenes, they were frantic to cover the tracks of a conspiracy that would lead to some of the presidents closest advisors. Nixon, for his part, was concerned that the FBI was delving into “uncomfortable territory,” and decided that the CIA would be better equipped to take over the investigation from the FBI.

McCord would eventually break with the Nixon White House, and sent a letter to Judge John Sirica—presiding judge at the burglars’ trial—in which he said he and the other defendants had been put under “political pressure” to plead guilty and keep their mouths shut.

Tapes of Oval Office conversations had been discovered, and Nixon fought tooth and nail to prevent these discussions from being made public. He released some of the tapes, but not all of them.

In March 1974, a grand jury indicted seven of Nixon’s former aides and named the president as an “unindicted conspirator.” That summer, the Supreme Court ordered Nixon to turn over the remaining tapes, which he again resisted. By now, the House had lost its patience and drafted three articles of impeachment against Nixon for obstruction of justice, abuse of power and criminal cover up, and several violations of the Constitution.

Following a visit to the Oval Office by Arizona Sen Barry Goldwater who told the president that neither the House nor the Senate could support his administration any longer, Nixon resigned the presidency on Aug. 8, 1974.

Both presidents Ronald Reagan and George H.W. Bush faced impeachment threats, each time from Texas Rep. Henry B. Gonzales. Neither of these resolutions were taken up by the House Judiciary Committee.

President Bill Clinton in 1995 began an affair with 21-year-old White House intern Monica Lewensky. Over the course of a year and a half, Clinton and Lewinsky reportedly had several sexual encounters in the White House. In April 1996, Lewinsky was transferred to the Pentagon when she confided in a staffer named Linda Tripp about her affair.

In 1997, with the relationship over, Tripp began to secretly record conversations with Lewinsky. Another woman, Paula Jones, had also accused then Arkansas Gov. Clinton of sexual harassment, and, in turn, Lewinsky was subpoenaed to help corroborate Jones’ story about Clinton. The FBI—working with Whitewater special council Kenneth Starr—would place a wire on Tripp when she met again with Lewinsky. A few days later, the story broke and Clinton publicly denied the allegations in uttering the famous words: “I did not have sexual relations with that woman, Ms. Lewinsky.”

Starr would soon release his report—along with 18 boxes of supporting documents—to the House of Representatives in outlining the need to impeach Clinton. On Dec. 11, 1998, the House Judiciary Committee approved three articles of impeachment, and one week later, Clinton was impeached.

In February 1999, the Senate voted on whether to remove Clinton from office. The prosecution needed a two-thirds majority to convict, but failed to achieve even a bare majority. Forty-five Democrats and 10 Republicans voted “not guilty” on the charge of obstruction of justice. Clinton told the public that he was “profoundly sorry” and went on to complete his second term of office.