Sen. Lindsey Graham sparked an uproar this weekend by suggesting Donald Trump Jr. should ignore a subpoena issued by the Senate Intelligence Committee.

During an interview on Fox News Sunday, the South Carolina Republican, said he believed the subpoena from the GOP-led panel was based on testimony from Trump's former personal attorney Michael Cohen, who is now serving a three-year sentence in federal prison for lying to Congress, among other charges.

"Anything based on what Michael Cohen said is worthless testimony. Michael Cohen is a worthless witness, and if I were Donald Trump Jr.'s lawyer I would tell him, 'You don't need to go back into this environment anymore, you've been there for hours and hours and hours. And nothing being alleged here changes the outcome of the Mueller investigation,'" Graham said.

"I would call it a day."

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On Monday, Graham told reporters he meant that Trump Jr. should invoke his constitutional right against self-incrimination rather than ignoring the subpoena altogether.

"You just show up and plead the Fifth and it’s over with," Graham said, according to The Washington Post.

"This whole thing is nuts," Graham added. "To me, it’s over."

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Graham has expressed support for Trump's belief that the investigation into potential ties between the Trump campaign and the Russian government's efforts to sway the election was a political "witch hunt."

On Sunday, Graham said he believes the FBI investigation – which led to the appointment of special counsel Robert Mueller – was a political "setup" from the beginning. Attorney General William Barr has opened an investigation into the origins of the Russia probe.

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"This is not the Lindsey I know," Sen. Joe Manchin, D-W.Va., said when on CNN Monday night about Graham's FBI conspiracy concerns. "Lindsey Graham has been a dear friend since I've been in the Senate. I can't explain what's going on right now in his thought process."

Manchin speculated that the death of Graham's close friend, Sen. John McCain, R-Ariz., "might have had some effect."

Manchin said Graham's advice to Trump Jr. was "wrong."

"For him to do and say the things that he has said here of late, doesn't make a lot of sense to us who have been close friends of his," he said.

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If Trump Jr. refuses to honor the Senate subpoena, it could lead to a debate among Republicans over whether to hold the president's son in contempt. The decision on such a vote would ultimately be left to Senate Majority Leader Mitch McConnell, who had declared the investigations into the 2016 election "case closed" before news of Trump Jr.'s subpoena surfaced.

McConnell said last week in a radio interview that Trump "ought not to worry" about the subpoena against his son.

Critics on social media have launched a campaign against Graham and called for his resignation along with a flurry of videos of his past statements that appear to contradict his current opinion of Trump and his position on impeachment.

One of the most often shared clips is from a CNN interview in which Graham implied Trump – who was then his rival for the Republican presidential nomination – was selling voters a false image of a tough businessman, when he was really a "race-baiting, xenophobic, religious bigot."

Twenty-year-old clips of Graham's calls for President Bill Clinton's impeachment have also resurfaced. In those videos, he disputes a number of defenses currently being offered against Trump's impeachment, including the notion that obstruction of justice can only occur if someone is trying to cover up a crime.

In one clip, Graham compared Clinton's refusal to comply with Congress to former President Richard Nixon's actions in the Watergate investigation. He said that one of the articles of impeachment against Nixon was based on his refusal to honor a congressional subpoena.

"The day Richard Nixon failed to answer that subpoena is the day that he was subject to impeachment," Graham said.

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