President Biden’s coronavirus vaccine mandates are hitting a pivotal moment, with federal courts emerging as a major obstacle to their implementation and the Senate poised to vote on a GOP-backed effort to defund the mandate on businesses.

Biden’s vaccine rules for private business, health care workers and federal contractors have all been tied up in court challenges from Republican officials, with some GOP-appointed judges blocking them.

Even if the administration ultimately wins the fights, the implementation of the rules could be delayed, potentially significantly.

The developments underscore the impact of the conservative-tilted federal bench, which was drastically molded by former President Trump in his tenure. Biden has hit the ground running trying to put his own mark on the bench, but legal experts say it will take years for the breadth of Biden’s own progress to be seen and his success in transforming the court depends on Democrats holding the Senate in 2022.

“It’s the bitter fruit of Trump,” said Carl Tobias, a University of Richmond law professor with expertise in federal courts. “This is where you are when Trump appointed almost a third of the federal appellate bench. This is what you’re going to see for some time.”

Health experts have reacted furiously to the rulings, saying that the delays would set back the U.S. in the progress against the virus.

“I think the health impact is disastrous, and I have no doubt that the judges who have blocked these rules will have caused many deaths,” said Lawrence Gostin, a public health law professor at Georgetown University, who argued the mandates have “strong legal backing” and attributed the rulings to “the political divisiveness of COVID-19 that has spilled over into the courts.”

The most recent activity came in the past week, when Trump-appointed judges in Missouri and Louisiana issued separate rulings blocking the Biden administration’s mandate for certain health care staff to be vaccinated against COVID-19 while court cases play out.

That caused the Centers for Medicare and Medicaid Services to suspend enforcement of the rule on Thursday “pending future developments in the litigation.” Under the rule, staff working in Medicare or Medicaid-certified providers were supposed to receive their first shot prior to Dec. 6 — Monday — and be fully vaccinated by Jan. 4.

And in Kentucky, a George W. Bush-appointed judge blocked Biden’s vaccine mandate for federal contractors in three states: Kentucky, Ohio and Tennessee.

“We are confident in the government’s authority to promote economy and efficiency in federal contracting through its vaccine requirement and the Department of Justice will vigorously defend it in court,” an Office of Management and Budget spokesperson said.

Republicans have mounted challenges to Biden’s vaccine mandates across the country, accusing the Biden administration of overstepping its authority. The state of Oklahoma also recently sued over the Pentagon’s vaccine mandate for the National Guard.

Thus far, conservative judges have been sympathetic to the challengers’ arguments.

“There is no question that mandating a vaccine to 10.3 million healthcare workers is something that should be done by Congress, not a government agency,” Judge Terry Doughty wrote last week in the U.S. District Court for the Western District of Louisiana in a ruling freezing the mandate for health workers. “It is not clear that even an Act of Congress mandating a vaccine would be constitutional.”

Last month, the Occupational Safety and Health Administration (OSHA), the agency within the Labor Department responsible for implementing the vaccine-or-test emergency rule for businesses with more than 100 employees, suspended enforcement of the rule after a ruling from the 5th U.S. Circuit Court of Appeals, one of the most conservative in the nation. The challenges to the rule have now all been consolidated at the 6th Circuit, which has 11 judges appointed by Republican presidents and five appointed by Democrats.

The mandate is supposed to take full effect on Jan. 4, with businesses then requiring employees to be fully vaccinated or submit to regular testing or face fines. The White House says that it is still working off the Jan. 4 deadline for the business and federal contractor mandates, but it’s unclear how long it will take for the case or the other similar legal disputes to be resolved.

Many legal experts see the fights going all the way to the Supreme Court, which could decide quickly by using its “shadow docket” or take longer by asking for a full briefing. The high court, which has a 6-3 conservative majority, could also decide to block the rules until it decides on the merits.

“Then that’s effectively killing it without ever saying it’s unlawful,” Gostin said.  

The developments have disappointed the White House, which has maintained it has the adequate legal authority and is urging businesses to move forward with vaccine-or-test rules regardless of the court action. Many businesses have implemented their own requirements and the White House has sought to lift them up as examples.

Tobias, however, said there is some argument to be made that the rule for businesses is “too much.”

“It seems like OSHA has done a pretty strong job of trying to justify by way of the requirements Congress imposed to justify this emergency power,” he said. “I think reasonable judges could differ on both the legal authority and whether the science is there to support what is going on.”

The administration has searched for other ways to encourage vaccinations, while staying clear of new mandates, though diminishing options remain to sway the quarter of eligible Americans who have thus far refused COVID-19 vaccines. 

Biden made a point during his remarks Thursday to note that his new plan to fight COVID-19 in the winter months, which includes efforts to promote booster doses and expand family vaccination clinics, did not incorporate any new mandates.

“While my existing federal vaccination requirements are being reviewed by the courts, this plan does not expand or add to those mandates,” Biden said, calling it “a plan that all Americans hopefully can rally around.”

The administration has not taken vaccine or testing requirements for domestic travel off the table, though Biden told reporters Friday he didn’t believe such a step would be necessary at this stage. Legal experts say such a step, too, would be sure to attract court challenges.

More immediately, the White House faces a threat of a Senate vote next week on a resolution to roll back the vaccine rule for businesses under the Congressional Review Act. Sen. Joe Manchin (D-W.Va.) has said he will support the effort, meaning it is likely to pass the Senate if all Republicans support it. The resolution faces a more uncertain fate in the House, where Democrats have narrow control.

“We disagree on that front and we’re going to continue to press forward with these requirements,” White House press secretary Jen Psaki said Friday when questioned about Manchin’s position. “I’m sure we will be having discussions with him and anyone who is an opponent of these steps.”

Psaki later acknowledged that companies are putting in place their own vaccine rules, but added, “we still feel at this point in fighting the virus it’s important to move forward with these requirements.”