Nearly 275,000 New Jersey residents are getting their health insurance coverage this year through Obamacare this year -- about 20,000 fewer people than in 2017, according to federal data released late Tuesday.

Public health experts expected a decline.

The Trump administration dramatically cut back on the amount of money spent promoting open enrollment season last fall.

Trump and Congress also fought for the better part of 2017 over how Obamacare should be repealed and replaced. The law remains intact, although under the federal tax cuts, the mandate that says people must buy a health insurance policy or face a fine at tax time will go away next year.

Nationally there are 11.8 million people insured through the state and federally run health exchanges, compared to the 12.2 million people in 2017, and 12.7 million in 2016, President Obama's final year in office, according to the U.S. Centers for Medicare and Medicaid Services.

CMS Administrator Seema Verma called the cuts to advertising a victory in cost-efficiency and described the decline enrollment as slight.

"The agency spent $10 million on marketing and outreach, which is just over $1 per HealthCare.gov enrollee by funding only the most efficient tactics and increasing direct response outreach. In comparison, last year CMS spent $11 per HealthCare.gov enrollee, totaling approximately $100 million to enroll nearly the same number of individuals that were enrolled this year," Verma said in a statement.

"Even with the success of this year's open enrollment, the individual market continues to see premiums rise and choices diminish," she added.

In New Jersey, the average monthly premium cost $575 this year, but the majority of people qualified for tax credits and paid an average of $234, according to CMS. Last year, the average monthly premium was $479 but with tax credits, people paid $206 a month.

Of the 274,782 New Jerseyans who bought a plan on the exchange, half are middle-age and older, from 45 to 64 years old. The youngest adult subscribers, in the 18 to 26 and 27 to 35 age brackets, made one up just a quarter of the enrollment.

Public health experts say even fewer young, healthy people will enroll next year when they no longer have to comply with the mandate. If so, premiums are expected to rise as only the older and sicker patients remain.

A bill is pending in the state Legislature to maintain the individual mandate to keep healthier people enrolled and head-off sharp premium increases.

Raymon Castro, a senior adviser for New Jersey Policy Perspective, praised the legislation, and Gov. Phil Murphy for "directing state agencies to provide whatever help they can within existing resources to help people to enroll."

"But without more funding for outreach and the individual mandate next year, enrollment will go down further," Castro said.

Susan K. Livio may be reached at slivio@njadvancemedia.com. Follow her on Twitter @SusanKLivio. Find NJ.com Politics on Facebook.