For four decades, Joe Biden opposed taxpayer funding of abortion as a fundamental matter of conscience. “I will continue to abide by the same principle that has guided me throughout my 21 years in the Senate: those of us who are opposed to abortion should not be compelled to pay for them,” Biden wrote to a constituent in 1994. “As you may know, I have consistently — on no fewer than 50 occasions — voted against federal funding of abortions.”

As he geared up for his ultimately unsuccessful 2008 presidential campaign, the Delaware senator reaffirmed this position in his book Promises to Keep: “I’ve stuck to my middle-of-the-road position on abortion for more than thirty years. I still vote against partial birth abortion and federal funding.”

As late as June 5, 2019 — six weeks after Biden formally launched his 2020 bid — his campaign said he still supported the Hyde amendment, a measure, attached annually to federal legislation, that prohibits federal tax dollars from funding elective abortions under Medicaid. But after 24 hours of pummeling by Democratic rivals and activists, Biden reversed himself the next day, announcing he no longer supported the Hyde amendment. His stated rationale for flip-flopping — that states were passing laws attempting to ban abortion — made little sense.

Biden’s abandonment of this core conviction because of political pressure is perhaps the lowest moment of his presidential campaign to date. As he had long said, those who understand that abortion is the taking of an innocent human life “should not be compelled to pay for them.”

Protecting conscience rights is indeed a weighty reason to support the Hyde amendment, but there is an even better reason to do so. What makes it the most important pro-life public policy since the Supreme Court’s 1973 Roe v. Wade decision is this: When you subsidize something, you get more of it, and this basic fact of social science holds true when that something is abortion.

One study by the Guttmacher Institute, a Planned Parenthood offshoot, found that in states that use their own tax dollars to pay for abortions undergone by Medicaid recipients, the abortion rate among Medicaid recipients is 3.9 times the rate among nonrecipients, “while in states that do not permit Medicaid funding for abortions, Medicaid recipients are only 1.6 times as likely as nonrecipients to have abortions.”

The precise number of lives saved by the Hyde amendment is a matter of dispute, but according to a 2016 report by the Charlotte Lozier Institute, an organization affiliated with the pro-life Susan B. Anthony List, “the best research indicates that the Hyde Amendment has saved over two million unborn children” since the policy was first enacted in 1976.

That’s an average of 50,000 human lives saved from abortion each year.

Ruth Bader Ginsburg acknowledged in a 2009 interview that a major rationale for funding abortions for Medicaid recipients was that it would result in a culling of the poor, though she put it a bit more euphemistically. “Frankly, I had thought that at the time Roe was decided, there was concern about population growth and particularly growth in populations that we don’t want to have too many of,” she said. “So that Roe was going to be then set up for Medicaid funding of abortion.” For that reason, the liberal Supreme Court justice said she was surprised that the Supreme Court did not strike down the Hyde amendment in the 1980 case Harris v. McRae.

After surviving that Supreme Court decision, the Hyde amendment was attached to bills funding Medicaid for four decades regardless of which party was in control of Congress and the White House. The first time around, in 1976, it was attached to an appropriations bill that Republican president Gerald Ford vetoed as exceeding his budget request; a supermajority of a Democratic Congress overrode the veto, thus enacting the policy into law. Jimmy Carter, Ford’s Democratic successor, supported the Hyde amendment. Democratic presidents Bill Clinton and Barack Obama officially opposed it, but there were enough moderate Democrats and pro-life Democrats in Congress that it survived overwhelming Democratic majorities in 1993 and 2009. (Although the prohibition on Medicaid funding for abortion survived the 2009–11 Congress, Democrats did expand federal subsidies for abortion via Obamacare exchanges in states that didn’t pass new laws banning such subsidies.)

But now, three factors mean that the Hyde amendment is in peril as never before.

First, the sitting Republican president’s response to the pandemic and the protests this summer has been so unpopular that Democrats are more likely than not to control the White House, the House, and the Senate in 2021.

Second, because of partisan polarization and Democrats’ purging of their own pro-life representatives, there are almost no supporters of the Hyde amendment left among congressional Democrats. In the Senate, Democrats Joe Manchin of West Virginia and Bob Casey Jr. of Pennsylvania both officially support it, but Republicans Lisa Murkowski of Alaska and Susan Collins of Maine oppose it. Even if the Democrats control the Senate by only a razor-thin majority, there would likely be majorities in both chambers to repeal the Hyde amendment.

Third, it is unlikely that filibuster rules would allow a GOP Senate minority to save the Hyde amendment in 2021.

If Democrats win control of the Senate, they may simply invoke the so-called nuclear option and eliminate the 60-vote threshold for all legislation. An increasing number of prominent Democrats, from Obama to Bernie Sanders, are calling for the abolition of the filibuster. Biden himself is now open to scrapping it.

Abolishing the filibuster would also give Democrats the opportunity to enact the Women’s Health Protection Act, a federal law that would invalidate almost all state laws on abortion, including bans on late-term abortion that lack exceptions on the basis of the woman’s emotional or mental health. Biden’s vice-presidential nominee Kamala Harris is a co-sponsor of the act, and although Biden said in 1997 that he would like to “ban all post-viability abortions,” he now speaks of his intention to “codify Roe v. Wade” into federal law. When congressional Democrats speak of “codifying” Roe, they mean enacting the Women’s Health Protection Act; but Biden has not been asked about that specific piece of legislation.

Even in a scenario in which a Democratic Senate does not nuke the filibuster in 2021, it is likely that congressional Democrats would still find a way to nuke the Hyde amendment.

The annual budget-reconciliation process already provides Congress the opportunity to pass legislation with a simple majority in the Senate. The GOP Senate used reconciliation in 2017 to pass its tax-reform bill, which also killed Obamacare’s individual mandate and opened up the Arctic National Wildlife Refuge to energy exploration.

It is true that budget reconciliation is subject to complex Senate rules about what may or may not pass with a simple majority, and it’s also true that in 2017 the Senate parliamentarian offered a preliminary opinion that adding Hyde-like protections to Obamacare’s exchanges would require 60 votes.

But it’s possible that Senate Democrats, without changing the rules at all, could come up with a creative way to provide unlimited taxpayer funding of abortion that would pass muster with the Senate parliamentarian, just as Senate Republicans found a creative way to pass a reconciliation bill defunding Planned Parenthood in 2015. As Oklahoma GOP senator James Lankford told National Review, “it is completely up to the parliamentarian on what they include and what they don’t include. So that’s somewhat of a wild card. It’s fairly subjective at times.”

If a Democratic Senate were to be thwarted by the parliamentarian in 2021, it could always overrule the parliamentarian. (Think of this as a “tactical nuking” of the filibuster.) If overruling the parliamentarian is necessary to enact, say, the “public Medicare-like option” that Joe Biden campaigned on, there is little doubt that Senate Democrats would do it. And if a Democratic Senate were to overrule the parliamentarian on any matter at all, they would also do it to kill the Hyde amendment.

Of course, unified Democratic control of the federal government is not a given in 2021. Polling now suggests Republicans are quite likely to lose the White House, but Democrats are only slightly favored to take the Senate.

Warning about the consequences of unchecked Democratic governance — on this issue and others — could improve GOP odds of holding on to the Senate. A poll conducted by Harvard for Politico on the eve of the 2016 election found that voters opposed repealing the Hyde amendment 58 percent to 36 percent.

Whatever else their merits, endangered Republicans can truthfully campaign on the fact that 51 warm Republican bodies in the upper chamber could be the only bulwark against unlimited taxpayer-funded abortion beginning in 2021.