With acting Defense Secretary Patrick Shanahan’s sudden withdrawal from the Senate confirmation process, Pentagon planners and nervous lawmakers are facing the reality that the world’s largest military might be without a permanent leader for several more months to come.

“For the sake of our national security, we need a confirmed Secretary of Defense — not just an acting,” Senate Armed Services Committee Chairman Jim Inhofe, R-Okla., said in a statement after Shanahan’s announcement Tuesday. “I hope we can get to that point as quickly as possible.”

Shanahan, 56, has served as the temporary head of the Defense Department since Jan. 1, when then Defense Secretary Jim Mattis was forced out of office ahead of his planned February departure date.

For the last several months, lawmakers have offered general support for Shanahan’s work in office but also repeatedly emphasized the need for a permanent replacement to guide military planning and priorities. President Donald Trump’s announced nomination of Shanahan to that role last month calmed many of those concerns.

Now, with the future of the leadership role again uncertain and tensions with Iran on the rise, those worries are resurfacing.

“This job should be filled in a matter of a few weeks, not months,” said Rep. Mac Thornberry, R-Texas, and ranking member on the House Armed Services Committee. “The uncertainty surrounding this vacant office encourages our enemies and unsettles our allies.

“Our country and our troops are facing an unprecedented array of threats around the world. We urgently need a secretary of Defense that has the confidence of the president, the Congress, and the country.”

Trump announced that Army Secretary Mark Esper would step into the acting defense secretary role in coming days. Senate Majority Leader Mitch McConnell, R-Ky., said praised Esper as a worthy temporary replacement, but added: “We’d be better off by far to have a secretary of Defense confirmed by the Senate.”

Inhofe has repeatedly urged Trump to nominate a permanent replacement for Mattis and warned Tuesday that a temporary defense secretary’s impact is lessened, particularly in interactions overseas.

“It’s bad,” Inhofe told reporters. “When you have the word ‘acting’ after your name, you’re not it, and you’re perceived by other countries as not being the person in charge.”

Shanahan withdrew from consideration amid reports of past domestic violence incidents in his family. Inhofe said Trump called to inform him personally, two hours before the announcement.

“There were some accusations that were different from before,” Inhofe said. “What he shared with me was they both agreed it’s going to get worse before it gets better, so just bail out.”

But several lawmakers on the Senate Armed Services Committee said they were not told of the allegations before the Senate confirmed Shanahan to the deputy post, One senior committee member — Sen. Jeanne Shaheen, D-N.H. — noted that “I would think the background check should have detected it.”

Inhofe indicated he had known about the allegations in a general sense. He defended the prior work, noting “there’s only so much you can do” and noting the reviews for most Pentagon jobs have shorter timelines than the defense secretary post.

Though Trump did not tell Inhofe he planned to offer Esper the formal nomination, Inhofe threw his support behind that idea.

“I’ve known him for a long time, I think he’s good. I’ve been in the field with him to see how he does with troops, and he’s exceptionally good,” Inhofe said, adding, “The president was very positive that he’s going to be acting. He thinks highly of him and he knows I do too.”

But the Senate’s No. 2 Democrat, Sen. Dick Durbin, of Illinois, noted that even if Esper is the pick, the confirmation for a new nominee will likely take “months,” as there are “critical questions to be asked,” about the administration’s national security policy.

"t’s a critically important position. It’s one of the top positions in our government. Filling it with someone who is competent, honest and has the right values is important,” Durbin said.

Congress is scheduled to be out for most of August, and getting the proper background checks and paperwork for a new nominee is unlikely to take place before then, even if Trump were to make a pick quickly.

When lawmakers return in September, they’ll also be facing several deadlines tied to the end of the fiscal year, including a budget impasse which could result in a partial government shutdown if a funding deal isn’t reached. That could further delay work on a defense nomination.

Before the start of this year, the Defense Department hadn’t gone without a permanent leader for more than 60 days since restructuring as a Cabinet level agency in the late 1940s. Tuesday marked the 168th day without one since Mattis’ departure.

In response to the Shanahan news, Senate Minority Leader Chuck Schumer, D-N.Y., blasted the administration for creating another layer of national security concerns in an already unstable world.

“To have no secretary of defense at this time is appalling,” he said. “It shows the chaos in this administration. They have so many empty positions, revolving doors in the most sensitive of security positions. Every American should worry.”