The Senate is heading toward a showdown with President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE over Saudi Arabia following last month’s killing of Washington Post contributor Jamal Khashoggi.

Senators are expected to force a vote as soon as this week to end U.S. support for Saudi Arabia’s military campaign in Yemen, marking the first test of the U.S.-Saudi relationship in Congress since the journalist’s slaying.

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If supporters are able to pass the resolution, it would be a significant break from Trump, who signaled last week that he is standing by the Saudi government.

Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE and Secretary of State Mike Pompeo Michael (Mike) Richard PompeoPutin nominated for Nobel Peace Prize The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Pompeo accused of stumping for Trump ahead of election MORE are scheduled to brief senators at 11 a.m. Wednesday, when they are expected to face a closed-door grilling as they try to persuade lawmakers to oppose the resolution.

Senate Foreign Relations Committee Chairman Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.) predicted that unless the administration can show that Saudi Arabia will pay a “price,” the resolution will likely have the votes needed to at least start debate.

“For people that want to speak to the issue of Yemen and Saudi Arabia and there’s no way otherwise to do it, this could turn out to be an appealing way,” said Corker, who later added that he “might well” vote to advance the resolution if the administration does not outline what steps it is taking.

Getting the legislation over the first hurdle, which will likely be a Republican motion to table it, would mark a political U-turn from March, when the Senate blocked the resolution. That measure called on Trump to withdraw any troops in “or affecting” Yemen within 30 days unless they are fighting al Qaeda.

At the time, supporters fell six votes short after the administration exerted a full-court lobbying effort to try to buy itself more time to show progress with Saudi Arabia. But frustration on Capitol Hill has boiled over in the aftermath of Khashoggi’s killing and sparked a growing foreign policy divide between congressional Republicans and the White House.

Supporters are stopping short of predicting success but say they feel more confident about their chances after previous votes were viewed as largely symbolic efforts to weigh in on foreign policy.

“Having run three of these resolutions through the Senate, the votes don’t tend to get fleshed out until about an hour before because so many of these issues are new” for some members, said Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.). “I feel more confident about this resolution than any one in the past.”

Ten Democrats voted to table the resolution in March. Murphy said they had flipped some of those lawmakers to supporting it.

Senators want CIA chief Gina Haspel, who examined Turkish evidence on the killing, to attend Wednesday’s briefing, but she is not slated to. The CIA has reportedly concluded that Saudi Crown Prince Mohammed bin Salman ordered Khashoggi’s death. But Trump pushed back on that notion last week.

“No, no, they didn’t conclude. I’m sorry. No, they didn’t conclude. They did not come to a conclusion. They have feelings certain ways. I have the report,” he said.

Sen. Bob Menendez Robert (Bob) MenendezKasie Hunt to host lead-in show for MSNBC's 'Morning Joe' Senators ask for removal of tariffs on EU food, wine, spirits: report VOA visa decision could hobble Venezuela coverage MORE (N.J.), the top Democrat on the Foreign Relations Committee, said that without an intelligence community official speaking at Wednesday’s briefing, he believes the Yemen resolution has a better shot of passing.

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Sen. Christopher Coons Christopher (Chris) Andrew CoonsMurkowski: Supreme Court nominee should not be taken up before election Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Del.), who like Menendez previously voted to table the resolution, described himself as a “likely yes.”

Several Republican senators who opposed the resolution in March are also remaining noncommittal about how they will vote. Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (R-Ariz.), a vocal critic of Trump, said he is “inclined” to support it.

When the vote will take place has yet to be locked down. Senators warn that if they are able to get on the measure it could become a “wild, wild west” of amendment votes on any number of foreign policy issues. That would open the door to senators potentially altering the legislation on the Senate floor, setting up the sort of unpredictable floor drama GOP leadership likes to avoid.

Sen. John Cornyn John CornynQuinnipiac polls show Trump leading Biden in Texas, deadlocked race in Ohio The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight MORE (Texas), the No. 2 Senate Republican, told reporters it would likely happen on Thursday. But it could be pushed to next week with the Senate currently working through a slate of nominations.

The fate of the resolution could be decided by the briefing with Mattis and Pompeo. Several senators acknowledged they are waiting until after they hear from them before deciding how to vote.

Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.), a sponsor of the legislation who is weighing another presidential bid in 2020, said, “Clearly the administration feels for whatever reason very close to the despotic regime in Saudi Arabia. … [But] I think most members of Congress are not prepared to support what Trump believes.”

Murphy added that the administration would “make every claim possible to stop this resolution from passing.”

Sen. Joe Manchin Joseph (Joe) ManchinSenate passes resolution reaffirming commitment to peaceful transition of power Hopes for DC, Puerto Rico statehood rise Manchin defends Supreme Court candidate Barrett: 'It's awful to bring in religion' MORE (D-W.Va.), who voted against the March resolution, said the Defense secretary convinced senators in March to table the resolution.

“I think that would be a harder argument to make now, so I’m anxious to hear from him,” Manchin said.

The administration leveled sanctions against 17 Saudis for their alleged role in the Khashoggi killing. But Trump said last week that “we may never know all of the facts surrounding” the homicide.

On Tuesday, White House press secretary Sarah Huckabee Sanders backed up the president’s claim, saying “we haven’t seen definitive evidence from our intelligence community that ties” the crown prince “directly” to the killing.

Despite momentum for the Yemen legislation, the administration has many GOP supporters on Capitol Hill who are skeptical of the pending measure.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellTrump 'no longer angry' at Romney because of Supreme Court stance On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline The Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power MORE (R-Ky.) said Tuesday that some sort of response would be “appropriate” and that Khashoggi’s killing was “completely abhorrent” but argued against completely cutting ties with Saudi Arabia, which he described as having a “pragmatic” relationship with the United States.

“Some kind of response certainly would be in order and we are discussing what the appropriate response would be,” McConnell told reporters.

“I’m going to vote ‘no’ because it affects our relationship with other countries,” said Sen. Lindsey Graham Lindsey Olin GrahamSteele Dossier sub-source was subject of FBI counterintelligence probe Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Key Democrat opposes GOP Section 230 subpoena for Facebook, Twitter, Google MORE (R-S.C.), an ally of the president who has been critical of Saudi Arabia following Khashoggi’s death. “I think it’s the wrong way to deal with this problem.”