BUENOS AIRES -- President Trump was headed to Argentina on Thursday to meet with fellow world leaders after a stinging setback from his own country's legislature over the killing of Washington Post contributor Jamal Khashoggi. A large majority of the Senate has pushed back against the president's defense of Saudi Crown Prince Mohammed bin Salman, who is suspected of ordering the murder.

The Republican-led Senate voted 63 to 37 on Wednesday to advance legislation which would end the U.S. military's support of the Saudi-led war in Yemen.

Even the president's close ally Sen. Lindsey Graham voted in favor, saying he changed his mind on the legislation, "because I'm pissed."

"The way the administration has handled the Saudi Arabia event is just not acceptable," Graham added, saying top administration officials' explanations thus far, did "not help me at all better understand the role" that Saudi Crown Prince Mohammed bin Salman played in the operation to kill Khashoggi.

As CBS News chief White House correspondent Major Garrett reports from the Argentine capital, Mr. Trump was arriving at the summit on Thursday facing a range of challenges -- both in Buenos Aires, and at home.

The Trump administration has promised to veto the withdrawal efforts advancing through Congress if they reach his desk in the form of a final bill.

The Senate vote came after a closed-door briefing by Secretary of State Mike Pompeo and Secretary of Defense Jim Mattis. Noticeably missing was CIA Director Gina Haspel, whose agency has overseen the Khashoggi investigation.

Graham, a Republican from South Carolina, called the meeting "inadequate," and threatened to withhold his vote from all pending legislation -- including a new government funding bill -- until the Senate receives a CIA briefing on the matter.

Secretary Mattis avoided questions about the Crown Prince's role in the murder after briefing the senators, telling reporters, "we have no smoking gun" that he was involved.

The Crown Prince himself, known by his initials MBS, arrived in Buenos on Wednesday. President Trump said he would meet with him, but there was nothing on the schedule.

Also on Trump's G-20 agenda

The president is to meet with Chinese President Xi Jinping, amid the prospect of a full-blown U.S.-China trade war.

Mr. Trump's top advisers have openly criticized Beijing for ignoring U.S. trade complaints, and yesterday both countries hurled new threats of higher tariffs and more economic uncertainty.

The president is also scheduled to meet Russian President Vladimir Putin here, but recent Russian naval aggression toward Ukraine could scuttle those talks.