Senate Republicans are warning President Trump against expanding the U.S. military offensive in Iran after he indicated he is willing to go as far as needed in order to complete the mission in the region.

GOP lawmakers largely backed Trump’s decision to order strikes against Tehran and other key locations over the weekend in coordination with Israel. But they indicated Monday they still have some major questions that need to be answered.

Headlining those are the timeline for the operation, the objectives and whether boots on the ground will be required to meet those objectives. Trump on Monday said in an interview he is open to that possibility if needed.

But with American casualties reaching six on Monday and conservatives warning of a second coming of the quagmire in Iraq, lawmakers are cautioning that there is peril if he goes that far.

“I think the president is well aware of the concerns of the American people for any kind of elongated engagement,” said Sen. Shelley Moore Capito (R-W.Va.), a member of GOP leadership.

“What I read [is] … be prepared for longer than what you think, it’s not a one-and-done situation,” she continued. “Anytime you have American lives that are lost or casualties, it becomes very tough and it’s almost deja vu to what we went through in the early 2000s.”

MAGA and conservative supporters for years have pointed to Trump’s key campaign pledge to end “forever wars” and keep out of foreign conflicts, but most have seemed to accept the administration’s actions last year in Iran and earlier this year in Venezuela.

But this latest effort is proving to be a tough one for them to swallow, especially after Trump’s declaration that he won’t rule out troops in the region.

“I don’t have the yips with respect to boots on the ground — like every president says, ‘There will be no boots on the ground.’ I don’t say it,” Trump told the New York Post after the strikes, which killed Iranian Supreme Leader Ayatollah Ali Khamenei and many other government leaders. “I say ‘probably don’t need them,’ [or] ‘if they were necessary.’”

“We’re already substantially ahead of our time projections. But whatever the time is, it’s OK,” Trump added on Monday at the White House. “Whatever it takes. … Right from the beginning, we projected four to five weeks, but we have capability to go far longer than that.”

Top Republicans still have major questions though, especially about who will run the country moving forward after Khamenei’s death, and the deaths of many of those who were considered possible successors.

The members of the Gang of Eight — composed of congressional leaders and relevant committee chairs — were briefed by Secretary of State Marco Rubio and other top administration officials on Monday.

The full Senate and House will similarly be briefed on Tuesday by officials, with lawmakers wondering what the next steps are in the region.

“What’s the endgame?” Sen. Chuck Grassley (R-Iowa) said in laying out the question he hopes officials are able to answer on Tuesday.

The Senate is expected to vote either later Tuesday or early Wednesday on a war powers resolution backed by Sens. Tim Kaine (D-Va.) and Rand Paul (R-Ky.). However, Kaine indicated that other than Paul and Sen. John Fetterman (D-Pa.), who is expected to vote “no” with Republicans, no other defections are expected.

Sen. Josh Hawley (R-Mo.) told reporters he will vote with the GOP on the resolution, arguing that the administration would need congressional authorization if troops end up being deployed.

“But that doesn’t seem to be in the immediate horizon,” he said.

However, that worry is still in the back of the minds of members. Sen. James Lankford (R-Okla.), a member of leadership, mentioned that sidestepping protracted conflict was among the main messages he’s heard from constituents in recent days.

“People don’t want a protracted war on it,” Lankford said. “But they’re also very concerned about Iran as well and the threats down there. So people are keenly aware.”

For now, Republicans continue to believe that despite Trump’s comments, boots on the ground in Iran are unlikely as the U.S. efforts continue to center on air support for the Israelis.

“I don’t think the president’s going to put boots on the ground. I’m not concerned about that,” Sen. John Kennedy (R-La.) said. “I think we’ll be able to accomplish all or most of everything we’re trying to accomplish without putting boots on the ground.”

Kennedy also said he did not believe it was fair to put a timeline on the efforts.

“This is what I know: Like it or not, President Trump believes in being a bear, and he believes if you’re going to be a bear, you ought to be a grizzly,” he said. “Now, he has made a decision. I think he will continue to do what he feels like he has to do until the mission is accomplished.” (The Hill)

Update news