WASHINGTON (AP) — As President Donald Trump clashes with the FBI over the planned release of a classified memo, former director James Comey has stood up for the bureau's position against the document's disclosure and taken aim at unnamed people he calls "weasels and liars."

"All should appreciate the FBI speaking up. I wish more of our leaders would," Comey tweeted Thursday night amid news that the FBI had lobbied the White House to block the release of a partisan memo on the Russia investigation.

On Friday morning, the president continued his verbal attacks against the FBI, writing on Twitter, "The top Leadership and Investigators of the FBI and the Justice Department have politicized the sacred investigative process in favor of Democrats and against Republicans — something which would have been unthinkable just a short time ago. Rank & File are great people!"

Trump and congressional Republicans have been attacking the FBI for its investigation of potential ties between Russia and Trump's 2016 campaign. Trump is expected to clear the way soon for the publication of a classified memo that Republicans say shows improper use of surveillance by the FBI in the initial stages of the investigation.

The Justice Department and Democrats have lobbied Trump to stop the release, saying it could harm national security and mislead the public.

On Twitter, Comey urged his former colleagues to "take heart: American history shows that, in the long run, weasels and liars never hold the field, so long as good people stand up."

He concluded, "Not a lot of schools or streets named for Joe McCarthy" — a reference to the senator who, in the 1950s, conducted hearings aimed at rooting out Communists in the U.S. government.

Since his firing last May, Comey has made his personal feelings about Trump known, testifying in detail about personal interactions he says troubled him.

He also authorized a close friend to share with reporters details from a memo he produced documenting one such encounter — a February conversation in the Oval Office in which he said Trump encouraged him to drop an FBI investigation into former national security adviser Michael Flynn. That revelation promoted the Justice Department's appointment of a special counsel to run the Russia investigation.

Comey has also used language about "weasels" before, most notably in a September 2016 congressional hearing when he defended the FBI's handling of the Hillary Clinton email investigation.

"You can call us wrong, but don't call us weasels," Comey said. "We are not weasels. We are honest people and we did this in that way."