Senate Intelligence Committee Chairman Richard Burr (R-N.C.) sparked infighting within the Republican Party last week after he subpoenaed Donald Trump Jr. to answer additional questions about the Russia investigation.

On Sunday, Senate Judiciary Committee Chairman Lindsey Graham (R-S.C.) advised Trump Jr. on the best way to proceed: Ignore the subpoena.

What did Graham say?

During an interview on Fox News' "Sunday Morning Futures," Graham said he respects Burr as his friend but dismissed the seriousness of the subpoena.

According to Graham, the subpoena is related to Michael Cohen and the infamous June 2016 Trump Tower meeting for which Trump Jr. was present.

"As I understand it, this subpoena relates to what Michael Cohen said about some meetings and about the Trump Tower in Russia," Graham explained. "All I can say is that Richard Burr is a very good friend. He's trying hard to be bipartisan. But anything based on what Michael Cohen said is worthless testimony. Michael Cohen is a worthless witness."

The South Carolina lawmaker went on to explain how he would counsel Trump Jr. if he were the younger Trump's lawyer.

"If I were Donald Trump Jr.'s lawyer, I would tell him, you don't need to go back into this environment anymore," Graham said. "You have been there for hours and hours and hours, and nothing being alleged here changes the outcome of the [Robert] Mueller investigation."

"I would call it a day," Graham exclaimed.

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It's not yet clear if Trump Jr. will comply with the subpoena. He previously testified before the Senate Judiciary Committee in September 2017.

A source close to Trump Jr. told the media last week that Trump Jr. is not happy with Burr's decision to issue the subpoena.

"When he originally agreed to testify in front of the Senate Intel Committee in 2017, there was an agreement between Don and the Committee that he would only have to come in and testify a single time as long as he was willing to stay for as long as they'd like, which Don did," the source said.

"Don continues to cooperate by producing documents and is willing to answer written questions, but no lawyer would ever agree to allow their client to participate in what is an obvious PR stunt from a so-called 'Republican' Senator too cowardly to stand up to his boss Mark Warner and the rest of the resistance Democrats on the committee," the source added.