Republicans have slated the FBI's decision not to recommend criminal charges against Democrat Hillary Clinton over her use of a personal email as US secretary of state from 2009 to 2013.
Paul Ryan, the speaker of the US House of Representatives and the highest elected Republican, said that the decision by FBI director "defies explanation" and that further information was needed about how the investigators reached this recommendation.
“No one should be above the law. But based upon the director’s own statement, it appears damage is being done to the rule of law,” said Mr Ryan.
“Declining to prosecute Secretary Clinton for recklessly mishandling and transmitting national security information will set a terrible precedent.”
He said that he expected the American people to “reject this troubling pattern of dishonesty and poor judgment”.
The FBI’s recommendation gives Mrs Clinton’s presidential hopes a boost by lifting a cloud that has overshadowed her campaign for more than a year.
FBI director James Comey’s rebuke of Mrs Clinton as being “extremely careless” for handling sensitive, highly classified information fueled further criticism.
Presumptive Republican presidential nominee Donald Trump, Mrs Clinton's rival in the November presidential election, tweeted in response to the FBI's decision: "The system is rigged. General Petraeus got in trouble for far less. Very, very unfair! As usual, bad judgment."
David Petraeus, who resigned as CIA director over an extramarital affair, was sentenced to two years’ probation and fined $100,000 last year after pleading guilty to passing classified information to his biographer, the woman he was having an affair with.
The Republican national committee questioned the impartiality of the FBI.
“As the Obama administration has repeatedly shown throughout this process, they were never going to prosecute Clinton’s criminal behaviour because they are counting on her to deliver their failed agenda a third term,” the committee said in a statement.
North Carolina event
The FBI's decision came just hours before Mrs Clinton joined Mr Obama on Air Force One to travel to North Carolina for his first appearance campaign for his former secretary of state.
It removes a major doubt around Mrs Clinton three weeks before Democratic delegates meet at the party's national convention in Philadelphia to confirm her as presidential nominee.
Shortly after Mrs Clinton’s use of a private email emerged in March 2015, she explained her use of a personal email account was for “convenience” as she thought “it would be easier to carry just one device for my work and for my personal emails instead of two.”
Mr Comey revealed new details around her private emails.
While Mrs Clinton and the State Department had insisted that none of the 2,000 emails later deemed classified were considered sensitive at the time, the FBI found that 110 emails in 52 email chains contained classified information at the time they were sent.
Investigators discovered several thousand work-related emails that were not among 30,000 emails turned over by Mrs Clinton to the State Department in 2014, some of which had been deleted.
The FBI found “no evidence that any of the additional work-related emails were intentionally deleted in an effort to conceal them,” said Mr Comey.
Some of her work-related emails “are now gone,” he said, because her lawyers deleted all emails they did not hand over to the State Department and “the lawyers cleaned their devices in such a way as to preclude complete forensic recovery.”
The FBI director concluded that while there was evidence of “potential violations,” there not enough to bring a criminal prosecution, though he did not condone her behaviour.
“To be clear, this is not to suggest that in similar circumstances, a person who engaged in this activity would face no consequences,” he said.
“To the contrary, those individuals are often subject to security or administrative sanctions.”