U.S. President Donald Trump hands Chief of Staff Reince Priebus (R) an executive order that directs agencies to ease the burden of Obamacare, after signing it in the Oval Office in Washington, U.S. January 20, 2017. Also pictured is White House Staff Secretary Rob Porter (C). (Jonathan Ernst/Reuters)

The number of Americans signing up for coverage through HealthCare.gov dropped by a half-million for 2017, as efforts by President Trump and congressional Republicans to demolish the Affordable Care Act propelled the first enrollment decline in its history.

The lower total, with 9.2 million consumers choosing health plans in ACA marketplaces through the enrollment deadline Tuesday, marks a striking turnabout from the trend as the Obama administration neared its end — when sign-ups for coverage under the law were running steadily ahead of a year ago.

The volume plummeted, in particular, during the final week of the three-month enrollment season — falling from nearly 700,000 in 2016 to just over 375,000.

That last week traditionally is a peak time when eligible customers race to get ACA health plans, most of them with federal subsidies. This time, however, the Trump White House directed federal health officials to halt all advertising and other enrollment-outreach activities for the last six days of the sign-up period.

The administration partly retracted the directive the next day, but the seesawing decisions exacerbated what had already been considerable public uncertainty over whether ACA health plans will continue through all of 2017, though insurers have signed contracts requiring them to do so.

(Senate Committee on Finance)

The absence of the customary deadline surge “could very well be the result of tremendous confusion and uncertainty surrounding the future of the health law, as well as the last-minute pulling of some outreach advertising,” said Larry Levitt, senior vice president of the Kaiser Family Foundation.

[White House stops ads, outreach for last days of 2017 ACA enrollment]

The numbers released Friday ended speculation that the Trump administration might break with its predecessor’s practice of announcing soon after each enrollment season how many people had chosen health plans. But the figures immediately touched off a fresh spate of the partisan warring that has been building since Trump’s election handed the GOP its first realistic chance of fulfilling its goal of abolishing the 2010 law.

In sharp contrast to the praise that Obama-era spokesmen lavished on the final tallies, Trump appointees at the Department of Health and Human Services delivered a jab along with the numbers.

“Obamacare has failed the American people, with one broken promise after another,” an HHS spokesman said, noting that some insurers abandoned this year’s marketplaces while a popular and significant tier of ACA coverage increased an average of 25 percent. “We look forward to providing relief to those who are being harmed by the status quo,” the spokesman said.

The chairman of the influential Senate Finance Committee, Sen. Orrin G. Hatch (R-Utah), said: “Enrollment numbers are down, and costs are up. These cost hikes are exactly the reason why Republicans are committed to repealing and replacing Obamacare.”

But leading groups that support the law sought to portray the figures in a different light.

Ron Pollack, executive director of Families USA, a consumer health lobby, accused the administration of “sabotage” of the enrollment process by withdrawing some advertising and sowing confusion over the marketplaces’ future. Trump’s first executive order as president called for agencies to undo some ACA rules, Pollack noted.

Anne Filipic, president of Enroll America, which has worked to spread insurance coverage through the ACA, said: “The fact that in the face of opposition and controversy, millions of Americans continued to enroll is an incredible testament to the importance of Affordable Care Act coverage to families all across the country.”

That coverage is intended for individual and families who do not have access to affordable health benefits through a job, as well as for small businesses. The small-business numbers were not released Friday.

[Obamacare is the Affordable Care Act: So what’s in it?]

The new numbers span the 39 states that relied this year on HealthCare.gov, the website for the ACA’s federal insurance exchange. They do not count the number of people who signed up in the remaining states, which run their own marketplaces under the law.

One of those separate marketplaces, Washington Healthplanfinder, announced Thursday that its enrollment for 2017 increased by 13 percent — record growth. The District of Columbia’s insurance exchange has not released final numbers but said last month that its December enrollment was 47 percent higher than it was the previous year.

And Peter Lee, the executive director of Covered California, announced Tuesday that eligible state residents would have an extra four days to choose health plans so that they did not “get caught up in a wave of last-minute shoppers.”

State-level figures in the federal exchange show no clear relationship between jumps in insurance premiums and sign-ups for 2017.

Coverage does not take effect until customers begin to pay monthly insurance premiums. For this reason, and because eligibility fluctuates, enrollment has ebbed during the course of each year since the marketplaces first opened in 2014.

Of the 9.2 million people who enrolled in the 39 states using HealthCare.gov, one-third were new to ACA coverage, while the rest were repeat customers or were automatically renewed by the government.

For 2016, 9.6 million people chose health plans in what were then 38 HealthCare.gov states, and about 1 million more enrolled in Kentucky, which moved to the federal marketplace for 2017 after its Republican-

controlled government ended what had been one of the nation’s most successful state-run marketplaces.

The number of people using the federal website’s Spanish version also tumbled, from 1.7 million a year ago to slightly less than 1 million.