WASHINGTON -- Two key Senate committees have demanded information about U.S. President Donald Trump’s firing of the director of the FBI, suggesting deepening political problems for the White House.

Trump’s abrupt dismissal of James Comey last week stunned Washington. Comey had been overseeing the FBI investigation of ties between Trump associates and Russian officials, including former national security adviser Michael Flynn.

The Senate Intelligence Committee said on May 17 that it has asked Comey to testify and also has asked his replacement, Andrew McCabe, to turn over any notes or memos about communication between the White House and the Justice Department about the Russia investigation.

Meanwhile, the four top Republican and Democratic members of the Senate Judiciary Committee released a letter on May 17 asking McCabe specifically for a memo Comey reportedly wrote after meeting with Trump in February.

The New York Times and The Washington Post said Comey wrote in the memo that Trump had asked him to end the FBI investigation of Flynn, who resigned after misleading White House officials about his contacts with the Russian ambassador.

Another congressional panel, the House Oversight Committee, has also demanded information about the Comey memo.

The White House has denied the assertions made in the Comey memo, and Trump himself has repeatedly denied any improper contacts with Russian officials.

Speaking during a commencement ceremony at the U.S. Coast Guard Academy on May 17, Trump said that "no politician in history, and I say this with great surety, has been treated worse or more unfairly."