At the end of 2001, not long after George W. Bush became president, there were 40 million people across the globe living with H.I.V./AIDS, which was usually a death sentence for those who lacked access to treatment. Most people with H.I.V. lived on the continent of Africa, where 2.3 million died of AIDS that year. There were widespread estimates that 100 million worldwide would die of AIDS in the following 20 years if something wasn’t done to better distribute treatment.

To Mr. Bush’s lasting credit, he did something about it. Working with Democrats and Republicans in Congress, at a time when cross-party cooperation was still happening, he instituted a program that has saved the lives of millions of people who would otherwise have died of AIDS, with broad support from evangelical Christian groups and from the Catholic Church. Twenty years later, that program and its vital work is imperiled by members of a very different Republican Party who are eager to politicize a once-bipartisan issue and exploit the country’s divisions on abortion. And while the Catholic Church maintains its support, many evangelical leaders are now fighting against it.

The program, the President’s Emergency Plan for AIDS Relief, or PEPFAR, was developed by the Bush administration with medical experts like Anthony Fauci and Mark Dybul to get drugs and medical personnel to 15 countries, 12 of them in Africa, and Mr. Bush announced it in his State of the Union address in 2003. Over the next 20 years, PEPFAR became one of the most successful global health programs in modern history, multiplying the number of people on lifesaving treatment by 300 times, from 66,500 in 2004 to more than 20 million people in 54 countries in 2022. It saved 25 million lives and, by preventing mother-to child transmission, allowed 5.5 million babies to be born H.I.V.-free.

Support for the program has long been bipartisan, and many of those who urged the passage of the initial $15 billion expenditure were conservative Republicans or Christian evangelicals, who saw saving lives as part of their religious duty. “In adopting this proposal, we show the world that conviction and compassion go together, as we demonstrate that compassion is not a sign of weakness but of strength,” said Henry Hyde, a leading Republican congressman from Illinois. Dave Weldon, a conservative Republican congressman from Florida, helped sponsor the PEPFAR bill and praised it for allowing religious groups to get federal funds to fight H.I.V.

Both men had long been fervent opponents of abortion. Mr. Hyde wrote a long-lasting federal law, known as the Hyde Amendment, barring the use of any federal funds to pay for abortion, and Mr. Weldon was the author of the Weldon Amendment, a law that allows insurers to refuse to pay for abortions. During the PEPFAR debate, they won assurances in 2003 that the program would never pay for abortions, and there is no evidence that it ever has, since that would violate U.S. law.

But those kinds of promises are not enough for today’s right-wing extremists, who say they believe the Biden administration has a secret plan to use PEPFAR to promote abortions overseas. That’s false, as is the whole premise that abortion has something to do with fighting AIDS. But many of those activists now hold positions of power in the House and are holding up the reauthorization of the program, which is set to expire on Sept. 30. In a polarized climate, they are seeking ways to make even this apolitical, unquestionably effective effort seem partisan, egged on by organizations like the Heritage Foundation that thrive on partisan division.

Early on, there were restrictions on the program imposed by the religious right. The original program required that a third of all prevention money be dedicated to teaching chastity and fidelity, even in countries where transmission was mostly through drug injection. Studies showed that the abstinence effort never worked, but it was seen as a necessary compromise to get conservatives onboard. The abstinence requirement was removed in 2008.

Bipartisan support continued through three reauthorizations of the program. That ended this year, when Republicans took over the House with a slim majority that was beholden to the MAGA wing of the party, which has been looking for opportunities to damage any Biden administration priorities. PEPFAR became a target when the Heritage Foundation released a falsehood-ridden report in May saying the administration was using it as a “vehicle to promote its domestic radical social agenda overseas,” specifically abortion and L.G.B.T.Q. issues.

The report provided no basis for this claim, other than to cite a White House memo on President Biden’s overall efforts “to support women’s and girls’ sexual and reproductive health and rights in the United States, as well as globally.” Mr. Biden’s only policy move was to reverse a Trump administration policy that prevented federal money from going to any organization fighting AIDS that is also providing counseling on abortion. That is consistent with the position established under Mr. Bush, that the abortion battle had nothing to do with global health.

But the report lit a fire under the most fervent anti-abortion Republicans in Congress, including former supporters of PEPFAR. Representative Chris Smith of New Jersey, who sponsored the program’s reauthorization in 2018, wrote a letter to his House colleagues saying the administration’s latest PEPFAR action plan “makes absolutely clear that the new direction of the program includes ‘integrating’ PEPFAR with abortion promotion.” That new direction is nowhere in the report. The White House even added a footnote to the document cited by Mr. Smith to make it explicitly clear that “PEPFAR does not fund abortions, consistent with longstanding legal restrictions on the use of foreign assistance funding related to abortion.”

Mr. Smith and several anti-abortion activist groups say they’re upset that some of the nonprofit groups getting PEPFAR money have separate efforts, not funded by the program, that provide or promote abortion. But that was also the case at the beginning of the program.

With the demise of Roe v. Wade and a resulting backlash among many voters, the far right’s anti-abortion demands have become increasingly outrageous. In the Senate, Tommy Tuberville of Alabama has held up all military promotions for half a year in a one-man crusade against the Pentagon’s policy allowing military personnel to travel to get an abortion.

Turning up the pressure, anti-abortion organizations like Susan B. Anthony Pro-Life America and the Family Research Council are making a test vote out of the reauthorization of PEPFAR, scoring it as a vote for abortion rights. That means any supporters of the program in its current form won’t get a perfect score on their anti-abortion report card, a threat strong enough to prevent many Republicans from doing the right thing. Mr. Smith and others want to add a policy cutting off AIDS funds to groups that provide abortion counseling, which could send reauthorization to defeat.

A failure to reauthorize PEPFAR wouldn’t kill it outright, unless the House separately refuses to appropriate money for it. But it would eliminate some of the rules that ensure the program’s funds go to the right places. More important, a no vote would send a clear signal to the rest of the world that it could no longer rely on the country to defend its reputation and its biggest accomplishments as a leader in global health. Even a program that once represented the highest ideals of the United States — its compassion, its expertise and its resources — is becoming a casualty of the country’s most destructive and divisive forces.