New York City Mayor Bill de Blasio is rushing to sign up 50,000 eligible New Yorkers for Obamacare before President-elect Donald Trump can fulfill a campaign promise to repeal the health-insurance law.

The Democratic mayor said he believes a repeal is less politically palatable for Trump if additional people are signed up. He added that more insured New Yorkers means a healthier population and lower costs to the taxpayer, who must pay to treat the uninsured at city-run emergency rooms.

“The more and more Americans that sign up for the ACA, the harder it is to take it away,” de Blasio said, using an abbreviation for Obamacare’s formal title: the Affordable Care Act.

Congressional Republicans have promised to begin to repeal President Barack Obama’s signature health care law soon after Trump is sworn in, with the effective date delayed several years for a full phaseout.

De Blasio announced the push at a city-owned medical facility on Manhattan’s Lower East Side.

At his side: an unemployed social worker insured by Obamacare, a cancer-stricken porter who would be uninsured but for the government-sponsored program, and an HIV-positive city councilman who recounted his yearslong struggle to navigate the health care system before he had city medical coverage.

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“What the Republicans and the president-elect are proposing is immoral. It is immoral! People’s lives are at stake,” said the councilman, Corey Johnson (D-Manhattan).

De Blasio aims to enroll about 50,000 through 2017 of the 500,000 eligible uninsured population in the city. New Yorkers can reach the program by visiting a #GetCoveredNYC venue, calling 311 or texting CoveredNYC to 877-877. De Blasio estimated the cost for ads and door-to-door outreach to be about $8 million.

The current enrollment period ends Jan. 31. Costs depend on income, starting at free for the poorest New Yorkers. People in the United States illegally are ineligible.

Stanley Brezenoff, interim head of the city’s public hospital system, said enrolling the 50,000 uninsured could save the city as much as $40 million.

De Blasio bemoaned the “sworn commitment to destroy” Obamacare by Trump and the national GOP. Since Trump’s election last month, de Blasio has promised to try to protect New Yorkers from Trump’s campaign agenda, such as curbing funding to abortion-provider Planned Parenthood, creating a Muslim registry and rounding up and deporting immigrants in the country illegally.

“Well, we can’t take that lying down,” de Blasio said. “We as New Yorkers need to fight back.”

A Trump representative did not return a message seeking comment.

The number of uninsured adult New Yorkers dropped to about 12.6 percent from about 21 percent soon after the health care legislation became law, according to the city health commissioner, Dr. Mary Bassett.