WASHINGTON — President Biden’s administration formalized a policy Friday opening Obamacare health insurance exchanges to people who arrived illegally in the US as children and have Deferred Action for Childhood Arrivals (DACA) status — at an estimated cost of up to $300 million per year.

The change, pending since last year, is projected to ease access to insurance and federal subsidies for roughly 100,000 uninsured DACA status holders and could soften the blow to pro-immigration advocates if Biden tries to curb record-high illegal immigration before the Nov. 5 election.

An official cost estimate from the administration projected $240 million in additional federal expenses in 2025 that will increase to $300 million in 2026 as a result of the change, made through a tweak to the definition of “lawfully present” for the purposes of accessing Affordable Care Act exchanges.

“This landmark final rule will make DACA recipients eligible for the Affordable Care Act coverage for the first time. It is projected to help more than 100,000 DACA recipients gain coverage,” an administration official said on a press call.

“By providing new opportunities for quality, affordable care healthcare, this rule will give DACA recipients that peace of mind and opportunity that every American deserves.”

Stephen MIller, former adviser to President Donald Trump and a prominent immigration hardliner, tweeted Friday that the change meant “[f]ree federal healthcare subsidies for ILLEGAL ALIENS — paid for by YOU.”

A White House official said that despite the price tag, “Congress will not have to appropriate additional funding as a result of this rule.”

The DACA program was created in 2012 by then-President Barack Obama when the DREAM Act failed to pass the Senate. It grants eligible applicants access to deportation protection and work permits.

Recipients pay taxes like US citizens and green-card holders, but are not able to easily gain permanent lawful status.

In 2017, Trump attempted to scrap DACA while saying Congress should approve a similar program. The Supreme Court overruled his order in 2020.

There were fewer than 600,000 DACA recipients as of last year, down from a peak of more than 700,000.

Immigration is one of the 81-year-old Biden’s top liabilities in his anticipated rematch against Trump, who is vowing to launch a mass deportation campaign after unprecedented illegal immigration under Biden.

Under Biden, most people who illegally cross the Mexican border are allowed to enter the US to pursue asylum claims in a move Republicans say encourages others to follow.

Shortly after taking office, Biden halted construction of Trump’s US-Mexico border wall and terminated the “Remain in Mexico” policy that required asylum seekers to await rulings on their claims of persecution south of the border.

The DACA benefits expansion comes amid reporting that Biden may seek to demonstrate a tougher approach to the border as polling shows the issue as a major election liability.

An Associated Press poll last month found that 56% of respondents said Biden made “immigration and border security” worse.

Biden claimed in January that he would “shut down the border until it could get back under control” if Republicans agreed to pass a reform package, but conservatives balked, saying Biden already had that authority, and he now reportedly is considering using it.

A record 2.5 million illegal immigrants were apprehended after crossing the southern border in fiscal 2023, which ended Sept. 30, followed by an all-time monthly record of nearly 302,000 in December.

Homeland Security Secretary Alejandro Mayorkas said in January that more than 85% of those detained for illegally crossing the border were being released into the US.