Sen. Lindsey Graham, R-S.C., on Thursday shot down President Donald Trump's demand that his predecessor, former President Barack Obama, be called to testify before Congress.
"I think it'd be a bad precedent to compel a former president to come before the Congress," Graham, a close ally of Trump's, told reporters on Capitol Hill.
"That would open up a can of worms and for a variety of reasons I don't think that's a good idea," Graham said.
But the senator does plan to hold hearings on matters related to the Russia investigation, he said in a statement Thursday.
Trump had tweeted earlier Thursday morning that, "If I were a Senator or Congressman, the first person I would call to testify about the biggest political crime and scandal in the history of the USA, by FAR, is former President Obama. He knew EVERYTHING."
Trump tagged Graham, chairman of the Senate Judiciary Committee, in the tweet: "Do it @LindseyGrahamSC, just do it. No more Mr. Nice Guy. No more talk!"
Trump did not say in his tweet what he thinks Obama should testify about.
The president has ramped up his attacks against Obama in the last week, after the Department of Justice's surprise move to dismiss its case against Michael Flynn, Trump's first national security advisor. Flynn had pleaded guilty to lying to the FBI about his conversations in the weeks before Trump's inauguration with then-Russian Ambassador Sergey Kislyak.
Over the weekend, Trump used the term "Obamagate" amid a slew of tweets and retweets attacking the FBI's conduct in Flynn's case.
The phrase appears to serve as a catchall for multiple allegations against Obama and former Vice President Joe Biden, who is now the apparent Democratic presidential nominee, which NBC News reported are not backed up by evidence.
Trump has long described former special counsel Robert Mueller's investigation of Russian election meddling, possible Kremlin coordination with Trump's 2016 campaign and possible obstruction of justice by the president himself, as a "hoax."
When a reporter at the White House on Monday asked what crime Trump was accusing Obama of committing, the president did not specify.
"You know what the crime is," Trump said. "The crime is very obvious to everybody. All you have to do is read the newspapers, except yours."
Last Friday, Yahoo News published audio of Obama saying in a private call that the Justice Department's move to drop its prosecution of Flynn made him worry that "the rule of law is at risk."
A spokeswoman for Obama did not respond to CNBC's request for comment on Trump's Thursday morning tweet.
Graham plans to hold congressional hearings in June regarding Flynn's case and other aspects of the Mueller probe, including whether Mueller "should have ever been appointed as Special Counsel."
Graham said in his statement that he plans to hold congressional hearings in June regarding Flynn's case and other aspects of the Mueller probe, including whether Mueller "should have ever been appointed as Special Counsel."
"To say we are living in unusual times is an understatement," Graham's statement added. "We have the sitting president (Trump) accusing the former president (Obama) of being part of a treasonous conspiracy to undermine his presidency. We have the former president suggesting the current president is destroying the rule of law by dismissing the General Flynn case."
If Graham or another senator were to subpoena Obama to testify, it would be a move made apparently without precedent in U.S. history. However, some former presidents and a small handful of sitting presidents – including George Washington and Abraham Lincoln – have voluntarily testified under oath, JustSecurity reported.
-- CNBC's Christina Wilkie contributed to this report.