On Wednesday, FBI Director James Comey failed to disclose whether the agency is investigating any ties between the Trump campaign and the Russian government.
Sen. Sheldon Whitehouse (D-RI) said Comey "failed to meet agreed upon deadline to confirm existence of FBI inquiry into Russia/Trump by this afternoon," according to CNN congressional reporter Manu Raju.
But Comey will reportedly be meeting with Senate Judiciary Committee Chair Chuck Grassley and Ranking Member Dianne Feinstein (D-CA) to discuss any potential investigations.
Senator Lindsey Graham (R-SC) and Whitehouse had urged Comey to reveal whether the agency has started a probe into the Trump administration's alleged ties to Russia—as well as the nature and scope of the investigation. Both senators said they had given the FBI head a March 15th deadline.
On Wednesday, Graham also threatened to subpoena any documents related to President Trump's claim that Trump Tower had been wiretapped, according to the Hill.
"He hasn't answered that letter. If he doesn't answer it today, I'm going to go to the chairman of the [Judiciary] Committee, Sen. Grassley, and seek his support to subpoena," Graham said on Fox News.
Comey faced pressure on other fronts. On Tuesday, Grassley said he'd delay that nomination of Trump's pick for deputy attorney general until Congress gets more clarity on the FBI's investigation into Russia's role in influencing the election.
The FBI director is also set to testify in a public hearing in the House Intelligence Committee on Monday, March 20th, according to Politico.
Graham said Wednesday afternoon that Comey has offered a classified briefing some time in the future in regards to information related to Trump Tower surveillance.
(Note: This article has been updated.)