A top House Democrat is pressing Republicans to reveal why they relied on the "sinister" allegations of a now-federally indicted FBI source in their Biden impeachment investigation.

Why it matters: The Justice Department charged Alexander Smirnov last month with lying to the FBI when he alleged that President Biden and his son Hunter were involved in a bribery scheme in Ukraine.

• Rep. Jamie Raskin (D-Md.) is now asking Republicans to explain why they were a "mouthpiece for lies likely concocted and promoted by Russian intelligence services," according to a letter first obtained by Axios.
• Republicans elevated Smirnov's claims in their impeachment probe, releasing an FBI document containing his allegations last year against the wishes of federal officials.
• Smirnov has "extensive foreign ties" to Russian intelligence agencies and foreign intelligence services, according to federal law enforcement.

The big picture: The Smirnov indictment was one of the biggest blows to the GOP impeachment probe, which appears to be unlikely to result in impeachment charges against Biden.

• House Judiciary Committee Chairman Jim Jordan (R-Ohio) said in January that Smirnov was a "highly credible" source for the investigation.
• The Justice Department says Smirnov has been "actively peddling new lies" aimed at affecting U.S. elections since November, when investigators allege he met with Russian intelligence officials.

Driving the news: Raskin demanded that House Oversight Committee Chairman James Comer (R-Ky.) release documents and communications related to his decision to amplify Smirnov's claims.

• "There was indeed a Russian hoax — a hoax by Russian intelligence and Vladimir Putin to pin utterly false smears on Joe Biden," Raskin wrote.
• "Please explain how our committee came to be used in this sinister campaign."

Raskin also asked Comer to release any documents that show the efforts of third parties to encourage or "coax" the chairman to release Smirnov's allegations against the Bidens.

What they're saying: A spokeswoman for Comer said the FBI told lawmakers that Smirnov was "credible and trusted."

• "The FBI kept the identity of its source secret from Congress while telling members of the Oversight Committee the confidential human source was credible and trusted, had worked with the FBI for over a decade, had been paid six figures, and was being used in ongoing investigations," the spokeswoman said.
• "Ranking Member Raskin knows this but he is again playing Biden defense attorney by trying to distract from the evidence this committee has unearthed revealing the Bidens' corruption."