Two senior Democrats want Deputy Attorney General Rod Rosenstein to resign if he declines to install a special prosecutor to lead the investigation into Russia’s interference in the 2016 presidential election.

Senate Minority Whip Dick Durbin (D-IL) and Senate Judiciary Committee ranking member Dianne Feinstein (D-CA) on Friday cautioned that President Donald Trump’s sudden dismissal of FBI director James Comey can’t allow the probe to be derailed.

“In an interview with NBC News, President Trump admitted to firing FBI Director James Comey because of his investigation of the Trump campaign’s Russian connections,” Durbin said in a statement. “That is dangerously close to obstruction of justice. This morning, the President tweeted a thinly veiled threat to Mr. Comey, which could be construed as threatening a witness in this investigation, which is another violation of federal law.”

Trump admitted to NBC that “this Russia thing with Trump and Russia” was on his mind when he decided to fire Comey, calling it a “made up story.”

After reports came out about a January dinner in which Trump reportedly asked Comey to pledge his loyalty to him, the President tweeted that the former FBI Director “better hope” there were no recordings of their conversations.

In her own statement, Feinstein said she supported “Durbin’s call for Deputy Attorney General Rod Rosenstein to resign if he is unwilling to appoint a special counsel.”

“These investigations are far too important to risk disruption, delay or interference,” she added.

The Trump administration initially attributed Comey’s dismissal to a memo Rosenstein wrote condemning the FBI director’s management of the probe into Hillary Clinton’s private email server.

The career prosecutor was appointed by Trump in January and only confirmed by the Senate in late April.