Sen. Lindsey Graham, R-S.C., said Wednesday that he is willing to hold up Congress' agenda -- including a spending bill meant to avert a partial government shutdown -- until the Senate hears from the CIA about the murder of Saudi activist Jamal Khashoggi.

"I'm not going to be denied the ability to be briefed by the CIA," Graham told reporters. "Anything that you need me for to get out of town, I ain't doing it until we hear from the CIA."

Senators were briefed about Khashoggi's death by Secretary of State Mike Pompeo and Secretary of Defense James Mattis. But Graham said the briefing was "inadequate" because no one from the CIA attended. U.S. intelligence officials have concluded that the Saudi crown prince, Mohammed bin Salman, must have at least known of the plot, the CIA's findings have not been made public and President Trump has equivocated over who was to blame.

Sen. Lindsey Graham, R-S.C. (AP)

"The question for me is whether or not the CIA supports the conclusion with a high degree of confidence that the crown prince was complicit in the murder of Mr. Khashoggi," Graham said.

Both Pompeo and Mattis said following the briefing that there was no direct evidence connecting the crown prince, known informally as "MBS," with Khashoggi's death. Both men also urged senators to vote against a resolution ending support for U.S. backing of Saudi-led forces in Yemen's civil war.

The White House issued a veto threat for that resolution, even as Pompeo and Mattis spoke with the senators. Emerging from the briefing, Pompeo said the vote would be "poorly timed" as diplomatic efforts to end the conflict were underway. In the briefing, the secretary of state argued that the war in Yemen would be "a hell of a lot worse" if the United States were not involved.

Hours later, the Senate voted 63-37 to advance the resolution. Graham initially voted against the measure, but then changed his mind and voted for it. After Graham switched his vote, he was seen shaking hands with Sen. Chris Murphy, D-Conn.

"I changed my mind [about the vote] because I'm pi--ed," Graham told Fox News outside the Senate chamber. "The way the administration has handled Saudi Arabia has been unacceptable ... Yemen is just one part of the puzzle. I think we have a right to be briefed by the CIA. How can I make an informed decision if I don't have access to the intelligence?"

In a Wall Street Journal op-ed published late Tuesday, Pompeo wrote that Khashoggi's murder "has heightened the Capitol Hill caterwauling and media pile-on. But degrading U.S.-Saudi ties would be a grave mistake for the national security of the U.S. and its allies."

Senate Majority Leader Mitch McConnell, R-Ky., said Tuesday that "some kind of response" was needed from the United States for the Saudis' role in Khashoggi's gruesome death.

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"What obviously happened, as basically certified by the CIA, is completely abhorrent to everything the United States holds dear and stands for in the world," McConnell said.

Sen Bob Menendez, D-N.J., the ranking member of the Senate Foreign Relations Committee, speculated that CIA Director Gina Haspel didn't attend the briefing because she "would have said with a high degree of confidence that the crown prince of Saudi Arabia was involved in the murder of Jamal Khashoggi."

In response to complaints about Haspel's absence, CIA spokesman Timothy Barrett said: "While Director Haspel did not attend today's Yemen policy briefing, the Agency has already briefed the Senate Select Committee on Intelligence and Congressional leadership on the totality of the compartmented, classified intelligence and will continue to provide updates on this important matter to policymakers and Congress. The notion that anyone told Director Haspel not to attend today's briefing is false."

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Khashoggi was killed Oct. 2 in what U.S. officials have described as an elaborate plot at the Saudi Consulate in Istanbul, which he had visited for marriage paperwork.

Trump has said it may never be known who was responsible for the killing, and in public comments — and a long and unusual statement last week — he reinforced the United States' long alliance with the Saudis. Trump has praised a pending arms deal with the kingdom that he says will provide the U.S. with jobs and lucrative payments, though some outside assessments say the economic benefits are exaggerated.

Fox News' Catherine Herridge, Kristina Biddle and The Associated Press contributed to this report.