Comey is expected to testify Wednesday before a subcommittee of the Senate Judiciary Committee, on which both senators serve.
Graham told TODAY that he met with Federal Bureau of Investigation director James Comey two weeks ago and asked him to hand over any evidence showing Trump was wiretapped during the campaign, as well as allegations about Russia's interference with USA elections.
"Congress is going to flex it's muscle here", said Graham.
Graham and Democratic Senator Sheldon Whitehouse, both Judiciary Committee members, asked Comey in a letter two weeks ago to provide the information by Wednesday. The pair are investigating potential attempts by Russian Federation to influence the 2016 election but are wary of interfering with any investigations the FBI is already conducting into the allegations.
After Michael Flynn resigned as national security adviser last month Grassley and the committee's ranking Democrat, Dianne Feinstein, formally requested a briefing on any related investigations, and transcripts of Flynn's calls with Russian Ambassador Sergey Kislyak. Obama administration representatives have denied the claim.
"I don't want to bump into a criminal investigation if there is one", he said.
USA intelligence agencies in January claimed that Russian President Vladimir Putin had ordered hacks of the Democratic National Committee's and Hillary Clinton's campaign chairman's computers to influence the election on Mr Trump's behalf.
Meanwhile, Graham also wants Comey and Justice Department officials to confirm whether a warrant was ever issued by the feds to wiretap Donald Trump's Trump Tower residence in NY prior to the election.
"I think if we don't get it today, the Congress is going to ramp up the pressure", Mr.
"I really don't know. We'll hold up the deputy attorney general's nomination until Congress is provided with [the] information to finally clear the air as to whether or not there was ever a warrant issued against the Trump campaign", he said on NBC's "Today" show. I'm suspicious of it.