Correction: An earlier version of this editorial incorrectly reported the number of women who die in pregnancy or childbirth. The most recent figures from the World Health Organization indicate roughly 303,000 women died during and following pregnancy in 2015. This version has been corrected.

SOME SAY the “Mexico City policy” — a restriction on U.S. funds to international organizations that provide, advise or discuss abortions — looks like a game of ping-pong. Republican administrations implement the rule, and Democratic ones volley it back. If so, President Trump has come to the table with a tennis racket.

President Ronald Reagan first issued what’s known among its opponents as the “global gag rule” on abortion, which is meant to ensure that taxpayer dollars do not subsidize abortion indirectly by aiding organizations that provide or promote it. But Reagan limited its reach to family-planning assistance, mostly provided through the U.S. Agency for International Development. President Bill Clinton undid the rule. When President George W. Bush put it back, he added a provision to clarify that family-planning funds provided through the State Department were also on the chopping block. President Barack Obama undid that.

Now Mr. Trump’s executive order takes a giant leap beyond previous GOP incarnations: It’s not just family-planning funds that are at risk, but all global health assistance, including funds to combat tuberculosis, malaria and AIDS. That ramps up the amount of aid at stake more than 15-fold — from about $575 million per year to $9.5 billion. A draft of another executive order, which has yet to undergo federal review, would deal an even harsher blow by freezing funding to United Nations organizations that endorse abortion or sterilization.

Organizations that complied with Reagan’s Mexico City policy left poor women with little choice but to seek unsafe abortions, or to give birth to children they could not afford to care for. Those that continued to offer information about abortion found themselves stripped of the funds they needed to do their jobs, from contraceptive care to counseling about sexually transmitted diseases. Mr. Trump’s policy will inflict the same damage on far more programs and far more people.

Every year, roughly 303,000 women die in pregnancy or childbirth. More than 6 million children die before age 5. Marie Stopes International estimates that the loss of its USAID-funded services alone over the next four years will result in 6.5 million unintended pregnancies, 2.2 million abortions — many unsafe — and 21,700 maternal deaths.

The White House has not announced what funding streams are set to go dry under the new policy, or whether Mr. Trump will make any exceptions, but at least one official has signaled that the administration’s intent was indeed to broaden the stricture. If so, a bipartisan tradition of U.S. leadership in global health will come to a catastrophic end.