FBI Director James Comey told congressional leaders that the agency is reviewing a new set of emails that “appear to be pertinent” to an investigation of Hillary Clinton’s use of a private server.

His letter — coming just 11 days before the Nov. 8 election — immediately gave Clinton’s GOP rival Donald Trump new ammunition in his attacks on her use of a private email server and how she handled classified information.

In July, Comey announced that the FBI’s investigation was concluded with no charges filed against Clinton. But he was critical of the way that she used her private server while she was secretary of state, calling her “careless” in the handling of sensitive information.

It’s an issue that has dogged Clinton throughout the campaign. Although she has said that she takes responsibility for the use of a private server, Trump has contended that she broke the law, and his rallies frequently include chants from his supporters of “Lock her up!”

“In connection with a related case, the FBI has learned of the existence of emails that appear to be pertinent to the investigation,” Comey wrote. “I am writing to inform you that the investigative team briefed me on this yesterday, and I agreed that the FBI should take appropriate investigative steps designed to allow investigators to review these emails to determine whether they contain classified information, as well as to assess their importance to our investigation.”

At a New Hampshire rally, Trump said, “I have great respect for the fact that the FBI and the Dept. of Justice are now willing to have the courage to right the horrible mistake that they made.”

He also said, “It might not be as rigged as I thought.”

Comey’s letter was vague about exactly what triggered the additional review, or if the new emails were from Clinton. He did not give a time frame for the FBI’s review.

NBC News’ Pete Williams, citing sources, said that in the course of a separate investigation, authorities “came across a device” that included other emails, but they were not emails from Clinton. He reported that “senior officials” said there was no evidence anyone was withholding evidence.

The New York Times reported that the newly discovered emails were those discovered on devices once shared by Huma Abedin, a top Clinton aide, and her husband, Anthony Weiner. They are now separated. The FBI is investigating Weiner’s texting of illicit messages to an underage girl.

Comey’s letter immediately sent news networks into overdrive, and later into a semantic scramble over whether it meant that the investigation was actually reopened or whether this was a review.

Update: Clinton campaign chairman John Podesta called on Comey to provide the “full details” of what is being examined, calling the FBI director’s letter “extraordinary.”

“FBI Director Comey should immediately provide the American public more information than is contained in the letter he sent to eight Republican committee chairmen. Already, we have seen characterizations that the FBI is ‘reopening’ an investigation, but Comey’s words do not match that characterization. Director Comey’s letter refers to emails that have come to light in an unrelated case, but we have no idea what those emails are and the Director himself notes they may not even be significant.

“It is extraordinary that we would see something like this just 11 days out from a presidential election.

“The Director owes it to the American people to immediately provide the full details of what he is now examining. We are confident this will not produce any conclusions different from the one the FBI reached in July.”