Some members of Congress are skeptical of Saudi Arabia’s commitment to reinvigorate its air campaign and grow Arab ground forces against the Islamic State in Syria — even after the Saudi foreign minister made a series of personal visits on Capitol Hill this week.

Saudi Arabia said earlier this week it would be willing to commit ground troops to fighting the Islamic State, also known as ISIS. But the country’s promise is contingent on the United States increasing its own commitment to send more Special Operations forces into Syria to combat ISIS. And that has a few senators wondering if the Saudi help will actually materialize.

“I hear a lot of talk,” said Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.), when asked what he thought of the Saudis’ promise to commit troops.

Committee ranking member Ben Cardin (D-Md.) paused to consider his words when asked the same question. “We obviously will judge their commitment by what they deliver,” he said.

Corker and Cardin are two of about a dozen senators and two members of the House who spoke with Saudi Foreign Minister Adel al-Jubeir in Washington during a series of wide-ranging meetings, which homed in on the anti-ISIS campaign. That fight has reached a critical juncture, as the United States and Russia agreed Thursday to a halt in hostilities on the ground in Syria.

“We said that if the U.S.-led coalition is going to send ground troops into Syria, we are prepared to send special forces, so now we are waiting to see what the plan looks like,” Jubeir said in an interview this week. “But we have said yes, we’re prepared to provide special forces as part of the ground operations in Syria.”

Pentagon officials were particularly encouraged by the Saudi vow. The influential regional powerhouse’s troop commitments are potentially critical to bringing other Arab nations still on the fence on board.

In the last several weeks, Russian airstrikes have cut off key opposition supply lines and enabled an advance by pro-government forces, who now have the city of Aleppo under siege. Brett McGurk, the U.S. special envoy for the counter-ISIS movement, told House lawmakers Wednesday that Russia’s campaign was having “a detrimental effect” on the fight against ISIS.

Late Thursday, the United States and Russia agreed to a “cessation of hostilities” to get humanitarian aid to besieged areas to begin within the next week. It’s unclear whether allies on the ground will observe it.

The announcement came after coalition partner nations gathered in Brussels to hear Defense Secretary Ashton Carter outline the U.S. strategy. U.S. officials hoped the nations would agree to enhance their commitment to the cause.

But in Congress, many wondered why the Saudi regime was hinging its resources on the United States making the first move.

“I don’t know why the U.S. has to make the first move on the chessboard,” said Sen. Tim Kaine (D-Va.), who also met with Jubeir. “Whose region is this? And who has the principal responsibility with it? We want to be partners with nations in the region tackling their own terrorist threat, but the notion they will be producing only if we play the leadership role – it kind of makes me question, how did that get to be?”

Congress is currently grappling with questions of its own about the fight against ISIS – with the answers often breaking down along partisan lines. Kaine, one of the chief advocates for Congress to pass a new authorization for use of military force to fight ISIS, opposes broad expansion of U.S. ground forces in Syria and Iraq.

However, Sen. John McCain (R-Ariz.), who has already urged the United States to commit thousands of ground troops to the anti-ISIS campaign in Syria, sees no problem with the Saudis wishing to see if the United States will commit more of its own forces.

“We’d have to do something in concert with them — not first, not last, but with them,” McCain said.

Saudi Arabia’s commitment is potentially pivotal in securing the help of other nations, but recent congressional testimony from top intelligence officials shed some uncertainty on how strategically important the Saudi forces would be to the ISIS fight – especially at a time when they are committing significant resources to an ongoing war in Yemen. Saudi Arabia and the United Arab Emirates already pulled back on their participation in the anti-ISIS coalition’s air campaign in Syria as the fighting in Yemen intensified.

“I do not assess that the Saudi ground forces would have the capacity to take this fight on,” Marine Lt. Gen. Vincent Stewart, director of the Defense Intelligence Agency, told Armed Services Committee senators on Tuesday. “I think the idea is, how do you get more U.S. skin in the game?”

For many Republican senators, pushing the administration to commit more resources to an anti-ISIS strategy is something they want to see happen anyway.

“They’re not going to do something unless we’re doing it, but they will pull their weight in what we decide the coalition should do,” said Senate Intelligence Committee Chairman Richard Burr (R-N.C.). “I think what they said was a diplomatic way of saying when you get a strategy, we’ll participate.”