The fourth open-enrollment season for insurance marketplaces created by the Affordable Care Act ends Tuesday amid efforts by President Trump and congressional Republicans to repeal the law. (Healthcare.gov)

The Affordable Care Act’s fourth open-enrollment season drew toward its scheduled close at midnight Tuesday amid uncertainty over how much actions by the Trump administration to undercut the law had affected the number of Americans signing up for health insurance through its marketplaces.

As of Monday, grass-roots Get Covered America groups in three-dozen states had 30 percent fewer consumers requesting online appointments to get assistance in choosing health plans compared with a year ago, according to the nonprofit organization Enroll America.

It was unclear whether those 76,000 appointments meant that fewer people were actually signing up. There could have been more walk-in customers, for example, or more returning buyers who didn’t need any help or another possible explanation.

Despite a presidential executive order to relax federal rules under the ACA and seesawing decisions to stop and then partly restart consumer outreach, the new White House has not touched mainstays of the enrollment operation.

The HealthCare.gov website for the federal insurance exchange on which 39 states rely has continued to operate. “Last chance to enroll — Jan. 31,” the site’s familiar blue-and-white home page still said Tuesday, and consumers could still get questions answered at federal call centers across the country.

(Jayne Orenstein/The Washington Post)

By late morning, the volume of people using HealthCare.gov had grown large enough to prompt federal officials to intermittently deploy an online waiting list, known as “queuing,” until space opened for additional customers. Starting at about 7 p.m., the online waiting system was no longer needed.

Around 9 p.m., federal health officials announced that while the deadline of midnight Pacific time would remain for the website, a slight extension would be allowed for people using the federal exchange who were waiting to hear back from a call center. This was the same policy as last year, ending speculation that the new administration might be less lenient with last-minute enrollment.

The 2017 open-enrollment period could be the final one under the ACA, depending on what happens in Congress in coming months. President Trump and Republican lawmakers have said that dismantling the 2010 law is a top priority. Although there is no consensus about what will succeed it, they have said they want a smooth transition for the roughly 10 million Americans with individual health plans through the federal exchange and similar state-run marketplaces.

For now, the looming question is the short-term impact of the Trump administration’s anti-ACA rhetoric and the actions officials already have taken. “The ultimate arbiter will be the [enrollment] numbers,” said Jennifer Sullivan, Enroll America’s vice president for programs.

The last update from the Obama administration on Jan. 10 showed that 11.5 million people had chosen health plans for 2017 by Christmas Eve through HealthCare.gov and the state marketplaces. That was nearly 300,000 more than during the equivalent time a year ago.

In the days since Trump took office, Sullivan said, people assisting with enrollment across the country got an influx of questions from consumers unsure whether the law’s features remain intact. Some asked whether the ACA still requires most Americans to have health insurance or risk a federal fine.

(Alice Li/The Washington Post)

The executive order the president signed on his first night in office does not specify which regulations would be eliminated, but it calls for agencies to modify rules that place a financial burden on individuals, suggesting that enforcement of the law’s coverage mandate might be lifted. No ACA rules have been rewritten so far.

Last week, when the White House directed the Health and Human Services Department to stop all enrollment outreach activities, ACA proponents and insurers warned that the action was likely to suppress sign-ups by the most desirable customers — younger and healthier people who tend to act right before the deadline. Stung by the outcry, the administration partly reversed course, reinstating Twitter notifications as well as emails and robo-calls to potential ACA customers. It also permitted television, radio and digital ads that HHS already had paid to air if the charge could not be refunded.

As the three months of open-enrollment ends, one other unknown is how much the Trump administration will say about the final numbers. Outgoing Obama administration officials in HHS took the unusual step of announcing when future enrollment updates would be provided.

Their schedule called for a “snapshot” this Friday that would contain the full sign-up tally from the federal insurance exchange. A spokesman for the Centers for Medicare and Medicaid Services, the HHS agency overseeing much of the ACA’s implementation, said this week that those figures were still expected.