Senators are making clear that key aspects of the U.S.-Saudi relationship are on the line as they ramp up pressure on the Saudi Arabian royal family and President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE over the disappearance of U.S.-based journalist Jamal Khashoggi.

Top Republican senators are hopeful the Trump administration will heed their warning and act on the Senate’s request for the White House to conduct a statutorily required investigation into whether Saudi sanctions are needed.

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But some lawmakers are going a step further by talking about a possible clampdown on the military-to-military relationship that would include nixing arms sales and withdrawing support for the Saudi-led coalition fighting in Yemen’s civil war.

“I think the burden of proof is now on the Saudis to demonstrate that they were not participants in any way in harming, killing or kidnapping Mr. Khashoggi,” said Sen. Tim Kaine Timothy (Tim) Michael KaineDemocrats call for declassifying election threats after briefing by Trump officials Buttigieg stands in as Pence for Harris's debate practice Trump meets with potential Supreme Court pick Amy Coney Barrett at White House MORE (D-Va.), a member of the Senate Foreign Relations Committee. “The burden of proof is on them. They got to show it, and if they don’t show it, I think it will fundamentally change the nature of the relationship.”

Khashoggi, a U.S. resident, has not been seen since Oct. 2, when he visited the Saudi consulate in Istanbul to get paperwork for his marriage to his Turkish fiancée.

Khashoggi was an insider of the Saudi royal court before he became a fierce critic, particularly of Crown Prince Mohammed bin Salman. He has been living in self-imposed exile in the Washington, D.C., area since 2017 and writing columns for The Washington Post, many of which have criticized Prince Mohammed, who’s considered the day-to-day leader of Saudi Arabia.

Turkish officials say Khashoggi was murdered inside the consulate and dismembered there. Saudi officials say that’s a baseless allegation and that he left the consulate alive the same day he arrived.

Trump, who has fostered a particularly close relationship with Saudi Arabia, has expressed concern about Khashoggi and pledged to find out what happened.

“We have investigators over there and we're working with Turkey, and, frankly, we're working with Saudi Arabia," Trump said Thursday on Fox News. "We want to find out what happened. He went in, and it doesn't look like he came out. It certainly doesn't look like he's around."

In his first trip abroad as president, Trump visited Riyadh and announced plans to sell the $110 billion in weapons to the Saudis, casting it as a boon to U.S. industry.

During additional comments on Thursday about Khashoggi, Trump dismissed the idea of abandoning that arms deal.

“We don’t like it, and we don’t like it even a little bit,” Trump told reporters in the Oval Office about Khashoggi’s disappearance. “But as to whether or not we should stop $110 billion from being spent in this country — knowing they have four or five alternatives, two of them very good alternatives — that would not be acceptable to me.”

In an effort to force Trump to take action, most members of the Senate Foreign Relations Committee sent him a letter Wednesday night requesting he conduct an investigation under the Global Magnitsky Human Rights Accountability Act.

That law, enacted and then expanded during the Obama administration, says the president must conduct an investigation if requested by the leaders of the Foreign Relations Committee, and then report back to the panel on whether the U.S. will levy sanctions.

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.), who signed the letter, described the request for a Magnitsky investigation as a “pretty strong step.”

“They will be under immense pressure, immense pressure, if it’s determined that Saudi Arabia was involved, to sanction pretty severely the people who have been involved in this,” Corker said of the administration.

Corker, who says he has reviewed U.S. intelligence on the issue, has spoken about Khashoggi’s fate and Saudi responsibility in increasingly stark terms over the past few days.

He also told reporters Thursday that “everything indicates” the Saudis murdered Khashoggi.

Corker indicated he wanted the Magnitsky investigation to play out before he would consider measures such as halting arms sales or cutting off support for the Saudis in neighboring Yemen. But he said he does not think an arms sale would pass Congress at this time.

“I can assure you it won’t happen for a while,” he said of an arms sale. “I know that Congress will not let this idly go by. This is something that enrages people, as it should.”

If the administration notifies Congress of a new arms sale to Saudi Arabia, lawmakers would have 30 days to block it if they decide to take that aggressive step. Foreign Relations Committee ranking member 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 (D-N.J.) in June placed a hold on any future U.S. arms sales to Saudi Arabia because of the war in Yemen, where lawmakers are concerned about a mounting civilian death toll.

Menendez said Thursday he sees a “rising sense” of support in the Senate for curtailing weapons sales to the Saudis, though said it’s a “moot point” because of his hold.

Menendez also warned the administration to take the Magnitsky investigation seriously.

“I expect it to be a serious review ... wherever it leads,” Menendez said. “If the conclusion is that members of the Saudi government were engaged in the disappearance and/or murder of Mr. Khashoggi, there will be the consequences called for under Magnitsky. We can’t let even an ally believe that they have carte blanche to do anything they want.”

Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.), a Trump ally who signed the Foreign Relations Committee letter, said he “absolutely” thinks the administration will take the investigation seriously.

Graham compared the Saudis to Russian President Vladimir Putin and said the United States should take the same punitive measures against the kingdom as it has for Russia.

“We expect stuff like this from Putin, and we come down hard on him when he does it. So everything we did to Putin, I want to do to Saudi Arabia,” Graham said. “I would unleash the sanctions from hell. These people care about — they live opulent lifestyles, they care about their wallet. I want to make an example of this government if they did this so that anybody else thinking that you can have an alliance and we don’t care about our values, you’ll be mistaken.”

But he said he still does not agree with ending U.S. support for the Saudis in the Yemen war, saying the Khashoggi issue and the Yemen war are “two different things.”

“The Yemen war is a proxy war with Iran,” he 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.), who previously teamed up with Sens. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.) and Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (R-Utah) to force a vote on ending U.S. support for the Saudi-led coalition in Yemen, said another war powers resolution “certainly is an option.”

“I am very doubtful that the administration is going to use the Magnitsky Act to impose mandatory sanctions, so I think it’s going to be left to Congress to take some steps to make sure Saudi Arabia understands there’s consequences,” Murphy said.

Absent a notification to Congress on a new arms sale, he said, targeting the Yemen war makes the most sense as an avenue for lawmakers to take action.

“The Yemen campaign is predicated on our belief that the Saudis are telling us the truth about their intention to bomb civilians,” he said. “They are mostly likely not telling us the truth about what happened inside the consulate, so why would we believe them when they tell us they’re not intentionally bombing civilians in Yemen?”

The only member of the Foreign Relations Committee who did not sign Wednesday’s letter to Trump was Sen. Rand Paul Randal (Rand) Howard PaulRand Paul says he can't judge 'guilt or innocence' in Breonna Taylor case Overnight Health Care: Health officials tell public to trust in science | Despair at CDC under Trump influence | A new vaccine phase 3 trial starts Health officials tell public to trust in science MORE (R-Ky.).

Paul has separately vowed to force a vote on blocking arms sales the next time Congress is notified of one. He also penned an op-ed Wednesday for The Atlantic saying he will introduce legislation that would cut off U.S. military support to the Saudis.

“This week, I intend to introduce another measure to cut all funding, training, advising and any other coordination to and with the military of Saudi Arabia until the journalist Jamal Khashoggi is returned alive,” he wrote.

“This oppressive regime must be held accountable for its actions,” Paul added. “The United States has no business supporting it, either directly or indirectly.”