Photo: Andrew Harrer/Bloomberg via Getty Images

Here it comes again. The U.S. House will vote Tuesday, for the third time since 2013, on a national ban on abortions that occur after 20 weeks of pregnancy.

As on the previous two occasions, the Senate will block any action on the bill (which would need 60 votes to overcome a certain filibuster by most Democrats and at least a couple of Republicans). It is also blatantly unconstitutional under prior Supreme Court precedents. And it also is aimed at addressing a nonexistent crisis of late-term abortions (the CDC estimates that 98.2 percent of abortions occur by the end of the 20th week of pregnancy, and 96.9 percent by 17 weeks).

So why is this legislation coming up again? And for that matter, why have 20 states enacted versions of it, despite strong indications that it would never pass constitutional muster?

The short answer is that 20-week bans reflect a long-standing strategic decision by the anti-abortion movement to focus on a tiny number of late-term abortions, even though their ultimate goal is to ban the vast number of abortions that occur earlier, mostly in the first trimester of pregnancy. Coupled with lurid imagery and misinformation about the nature and frequency of late-term abortions, this strategy achieved the movement’s biggest-ever legal victory, the 2007 Supreme Court decision in Gonzales v. Carhart, in which a 5-4 majority upheld a congressional ban on so-called “partial-birth abortions,” defined as a specific abortion method (“intact D&E”) that Congress “found” never to be medically necessary.

Right-to-lifers recently refocused on late-term abortions when their advocacy of TRAP laws (Targeted Restrictions on Abortion Providers), designed to make life so difficult for abortion providers that they go out of business, ran into a brick wall at SCOTUS with the 2015 decision in Whole Women’s Health v. Hellerstedt, which made it clear the Court was not going to abandon the basic constitutional right to abortion set out by Roe v. Wade in 1973 and Planned Parenthood v. Casey in 1992.

The argument for a 20-week ban is the scientifically specious claim that a fetus can feel pain at the 20-week mark of pregnancy. Again, the number of abortions that occur between the 20-week mark and the 24 weeks typically advanced as the beginning of fetal viability — the standard for allowing restrictions on abortions in certain circumstances under Roe v. Wade — isn’t large at all. The aim here is precisely to undermine the viability standard, and with it any constitutional protections for the right to choose. But there is a second devious legal strategy as well: The proposed 20-week federal ban, like all the state bans, does not provide a broad exception for the health of the mother as determined by a physician, as required by the Casey decision; it also has a narrow and difficult-to-prove exception for rape and incest survivors, who must prove their own victimhood.

The fate of this and previous 20-week bans under the current Supreme Court was almost certainly indicated in 2014 when SCOTUS refused to take up an appeal to the Ninth Circuit Court of Appeals’ invalidation of a law passed by Arizona. If, of course, Donald Trump gets a second Supreme Court appointment to replace one of the five justices that voted in the majority in Hellerstedt (Kennedy, Ginsburg, Breyer, Sotomayor, or Kagan), all bets are off. And one rationale for passing 20-week bans in the states is to set up a challenge to abortion rights that can unfold on that great-gettin-up morning for the RTL crusade.

For now, though, the most immediate reason for pushing this doomed 20-week ban in the U.S. House is to provide a tonic for the troops, who are very frustrated by the failure of this Republican Congress to “defund” Planned Parenthood or ban use of federal subsidies for health-insurance policies that cover abortion services. Both those goals have gone down with the serial GOP efforts to repeal and replace Obamacare. So giving grassroots anti-abortion activists a new vote to whip is good for morale, while forcing members of Congress in both chambers to go on record yet again on this test of loyalties.

The case for 20-week bans is so full of evasions (of the actual goals of proponents), distractions (from the constitutional rights against which it transgresses), and plain lies (about “fetal pain” and the frequency of late-term abortions) that it’s not easy to advise pro-choice advocates how to respond to this phony war for a phony cause. The simplest response is to suggest that this is a bald challenge to a constitutional framework that has served women well for more than 40 years, and that 20-week-ban proponents would destroy instantly if they had the power to do so. They should not be given any traction for turning the clock back.