Ahead of the Senate’s return from August recess, Majority Leader Schumer and Senator Tuberville appear to be digging in in their standoff over Mr. Tuberville’s one-man blockade of military and Pentagon appointments and nominations.

Since March, Mr. Tuberville has been holding up hundreds of military and Department of Defense appointments, including some of the most senior generals overseeing entire branches of service, until the Pentagon ends its policy of reimbursing service members’ out–of-state travel costs to get abortions.

Over the break, Mr. Tuberville has shown no sign that he will back down from his hold despite being denounced by President Biden and top generals, insisting that he intends to keep up his protest until the abortion travel policy changes. Now, Mr. Schumer is doubling down on his refusal to bend to Mr. Tuberville.

“This is a problem created by Republicans, and it’s up to them to solve it,” Mr. Schumer told reporters. “We’re not going to shift the burden to Democrats when this is a Republican-caused problem.”

The stakes are only getting higher. General Mark Milley, the chairman of the Joint Chiefs of Staff and a senior military advisor to the president, is supposed to step down on October 1.

His replacement, General C.Q. Brown, is ready to take his place, but he will only be able to serve in an acting capacity until he is confirmed, which imposes some limitations.

There is a way around the blockade. Mr. Schumer could put certain nominations to the floor for individual votes, a laborious and time-consuming process that some Republicans on the Senate Armed Services Committee are pushing for the most senior appointments

The problem with the workaround is how long it would take. Confirming the more than 300 appointees that Mr. Tuberville has blocked would potentially take weeks in the Senate, and the upper chamber would have to sideline all other business to make the confirmation votes happen.

The other risk, for Democrats or any party in the majority, is that it would set the precedent that a single senator could extract major policy changes by simply blocking the Senate from conducting its business.

While there’s no end in sight for the standoff, there has been increasing pressure from those in the military to resolve the conflict, with the secretaries of the Army, Navy, and Air Force calling on Mr. Tuberville to drop his hold earlier this week.

In an op-ed in the Washington Post, the Navy secretary, Carlos Del Toro, the Air Force secretary, Frank Kendall, and the Army secretary, Christine Wormuth, implored Mr. Tuberville to end his blockade.

“Senators have many legislative and oversight tools to show their opposition to a specific policy,” the secretaries wrote. “But placing a blanket hold on all general and flag officer nominees, who as apolitical officials have traditionally been exempt from the hold process, is unfair to these military leaders and their families.”

In the op-ed, the secretaries go on to say that Mr. Tuberville’s hold is “putting our national security at risk” and that the hold is signaling that “service at the highest ranks of our military is no longer valued by members of Congress.”

Mr. Tuberville maintains that he, in holding military appointments until he extracts a policy change from the Pentagon, “didn’t start this.”

“The Biden Admin injected politics into the military and imposed an unlawful abortion policy on the American taxpayers,” Mr. Tuberville said in a statement last week. “I am trying to get politics out of the military.”