Democratic senator on GOP colleague Lindsey Graham in Trump era: He's been 'incredibly politically brave'
But as he explained in calling Graham a "great guy," Whitehouse, a Rhode Island Democrat, said that attribute is nothing new for the South Carolina senator.
"I think he's been his usual, incredibly politically brave self," Whitehouse said. "A lot of people, as Trump moved forward to becoming the nominee and the president-elect and the president, pulled pretty fast 180s in currying favor and trying to get back into Trump's favor."
"And I think Lindsey is a very principled person, and he's made his decision about this man," Whitehouse continued. "And he will accord him what respect is necessary, but he certainly is not going to go sniffling back begging for forgiveness and favor."
Whitehouse, who spoke with Business Insider this week while promoting his newly released book, "Captured: The Corporate Infiltration of American Democracy," is the ranking member of a Senate Judiciary subcommittee that is investigating Russia's role in the 2016 election. Graham is chairing the committee.
Several intelligence agencies concluded that Russia meddled in the election process to assist Trump, and reports have surfaced that several Trump campaign officials were in constant communication with Russian officials during the campaign, which Trump has denied awareness of. Additionally, Russia-related controversies led to Michael Flynn's resignation as national security adviser last week.
Trump has attempted to downplay the stories related to Russia, saying during a press conference last week that "Russia is fake news."
Graham, who did not endorse or vote for Trump, has long been one of the president's most vocal Republican critics - particularly as it relates to the Russia-related cloud hanging over the Trump White House.
"I think he's been deeply concerned as an American - as someone who's spent most of his life in uniform - that this is really bad stuff," Whitehouse said. "And, if something along these lines happened, this is something we have got to sort out. It is essential to our patriotism. Well beyond party, well beyond individuals and all that."