Senators met with Robert Mueller, who was named special counsel in an investigation involving Russia's meddling in the election of President Donald Trump, on Thursday. During Thursday's meeting, it led at least one senator to believe the probe has now turned into a criminal investigation.
Senator Lindsey Graham said before reporters, "It seems to me now to be considered a criminal investigation"
Graham said that the nature of Mueller's investigation has hurt the Senate's ability to call witnesses in their counter-intelligence probe.
When asked, Sen. Marco Rubio, R-Fla, would not confirm Graham's comments.
Earlier on Thursday, Trump tweeted, "This is the single greatest witch hunt of a politician in American history!"
At a press conference later on Thursday, Trump said, "I respect the move but the entire thing is a witch hunt. There is no collusion."
Mueller was named as special counsel on Wednesday, one day after a report surfaced that Trump had requested ex-FBI Director James Comey end any investigations involving National Security Adviser Michael Flynn's contacts with Russia.
Trump claimed that the report on Comey's memo was not true.
Comey was then fired by Trump as the investigation continued.
Originally, the Trump White House claimed that Comey was fired based on a recommendation from Deputy Attorney General Rod Rosenstein. Sen. Dick Durbin, D-Ill., said on Thursday that Rosenstein knew Comey would be fired before writing the recommendation.