A Democratic lawmaker from New York said Thursday it would be an "impeachable offense" if President Trump fired former FBI Director James Comey for refusing to end the investigation into Russia's meddling in the 2016 election.

"If the president fired Comey because he had asked for loyalty and hadn't gotten it, because he had asked him to ease off on the investigation of Flynn, because in effect he was asking him to ease off on the investigation of possible collusion by the Trump campaign with the Russians in subverting the election, that would be obstruction of justice, which is an impeachable offense," Rep. Jerry Nadler, said in an interview on CNN.

Trump fired Comey last month, and it was later revealed in news reports that the president had asked Comey to pledge his loyalty to him during a dinner days after his inauguration.

Trump also reportedly asked Comey to drop the FBI's investigation into Mike Flynn, the president's former national security adviser. Trump fired Flynn in February for misleading Vice President Mike Pence about his contacts with Russian officials.

The former FBI director memorialized his interactions with Trump in memos, and congressional investigators have asked the FBI to produce copies of those documents as part of their investigations into Trump campaign associates and their ties to the Russian government.

Nadler said that although Comey denied Trump's requests, the president still could face charges of obstruction of justice.

"Obstruction of justice does not have to be effective," he said. "It's an intent-based crime. We're not talking about a criminal thing here. We're talking about the process of obstruction of justice, and that would be a very serious thing to attribute to the president."

After Trump fired Comey, the Justice Department appointed former FBI Director Robert Mueller to serve as special counsel and lead the Russia probe.

The House and Senate Intelligence Committees are also investigating Russia's interference in the election, as well as ties between Trump associates and the Kremlin.

Nadler, though, said a special commission was needed.