Donald Trump is at war with the FBI over an investigation into possible collusion between his presidential campaign and Russia, but he isn't the first United States president to have trouble with the bureau.
The Federal Bureau of Investigation was created in 1908 by Theodore Roosevelt. In 1924, J Edgar Hoover became its director, and remained in that position until he died in 1972.
During his 48-year tenure Hoover developed a close relationship with almost all the presidents, most of whom were happy to give him unfettered power in exchange for information.
Franklin D Roosevelt, for example, wanted Hoover to give him a clear picture of the activities of American fascists and communists. He gave the FBI a mandate to conduct warrantless wiretapping, eavesdropping and break-ins.
It was this expansion of FBI power that frequently led to abuses by the FBI during the 1950s and '60s.
After Hoover's death a series of inquiries into the FBI led to a greater distance between the bureau and the presidency, and the FBI started to use its power to investigate the White House.
First came the Watergate investigation.
1. Richard Nixon
Richard Nixon once called Hoover his closest friend in all political life.
They formed an alliance in 1947 when Nixon was a newly-elected congressman, and that held for the better part of 25 years.
But it all ended in 1970, according to Tim Weiner, who wrote a book on the FBI's history.
"Hoover would not sign off on a plan … to unleash the full powers of the CIA and the FBI and the NSA … to take off any restrictions that the Constitution might impose and [allow them to] spy on anyone the president deemed a threat to not only the United States but his personal power," he said.
"Hoover wouldn't sign it because he felt that the geo-tectonic plates of American politics and American society were shifting to the left, and they were."
Enraged, Nixon set up his own organisation in the basement of the White House, a team largely made up of ex-CIA and FBI officials.
They became known as "the plumbers" — and it was these men who conducted the infamous break-in at the Watergate, six weeks after Hoover died.
Eventually, the FBI was the force that ultimately brought down Nixon during the Watergate scandal.
"[It] gathered the evidence against the president, and all the president's men, and brought them to justice, [enabling] the Watergate special prosecutor to name Nixon as an un-indicted co-conspirator in a case of obstruction of justice," Weiner explained.
2. Ronald Reagan
In mid-1980s, the bureau went after the Reagan administration over the Iran-Contra affair.
"[The affair] involved Reagan's National Security Council (with the president's approval) selling arms to Iran, skimming the proceeds, and giving them to anti-Communist guerrillas in Central America, in defiance of prohibitions passed by Congress," Weiner said.
"Twelve of Reagan's highest national security officials were eventually indicted in that matter."
The extent of Reagan's personal involvement and knowledge was never properly established, although he did publicly accept responsibility for the actions of his administration.
The affair initially damaged his public approval ratings.
But incredibly, by the time he left office in 1989, the public's confidence in Reagan had largely recovered, with one poll recording an approval rating of 64 per cent.
3. Bill Clinton
Bill Clinton was the next president to face the scrutiny of the FBI.
In 1998, at the request of the US Office of Independent Council (OIC), the FBI Laboratory tested the dress belonging to intern Monica Lewinsky, which she said was stained with the president's semen during a sexual encounter.
"The FBI famously went after Bill Clinton and wound up drawing blood from his arm in the White House," Weiner said.
The DNA from that blood, drawn from Mr Clinton by a White House physician in the presence of a senior OIC attorney and an FBI special agent, later proved he was lying under oath when he said he did not have sexual relations with Ms Lewinsky.
As a result, Mr Clinton was impeached by the US House of Representatives on charges of perjury and obstruction of justice.
He was acquitted on all counts by the Senate.
4. George W Bush
In the early 2000s, the FBI's then-director Robert Mueller made a stand against George W Bush after he authorised an illegal National Security Agency (NSA) program to eavesdrop on American phone calls without a warrant.
Together with acting attorney-general James Comey, Mr Mueller told the president:
"The NSA is spying on Americans in a way that violates the law and the Constitution."
Both men told Mr Bush if he didn't restrict his orders to the NSA to conduct this kind of espionage, they would resign.
A long struggle ensued, but eventually Mr Bush backed down and restricted the NSA's spying activities.
5. Donald Trump
Now Mr Trump is in the FBI's sights.
What Mr Mueller, as special counsel, has done and what we saw in the indictments is quite extraordinary, Weiner says.
"In both the case against Trump's former campaign manager Paul Manafort, and against the Russians who attacked this country, he has charged a conspiracy to defraud the United States," he said.
"And he has done so with a remarkable set of counterintelligence forensics that establish precisely what the Russians were doing in this country, and some terrific money-laundering work that established that Manafort, at the time of his appointment as Trump's campaign manager, had received in excess of $12 million from a crooked oligarch who was a friend of Putin's."
Weiner argues that Mr Mueller has laid the groundwork to establish that the firing of James Comey, who was conducting that investigation, constitutes an obstruction of justice.
If he is right and if Congress, in particular the House of Representatives, flips from Republican to Democratic, we may just see Congress once again impeaching a President.