Protesters on both sides of the abortion issue gathered outside the Supreme Court in Washington during the March for Life. CreditSusan Walsh/Associated Press

People who care about basic American freedoms should be grateful to the Senate majority leader, Mitch McConnell, for one thing: He has given liberals another good reason to flock to the polls in November.

Mr. McConnell is set to hold a procedural vote this week on a bill that would ban abortion at 20 weeks of pregnancy. The so-called Pain-Capable Unborn Child Protection Act, sponsored by Senator Lindsey Graham, a South Carolina Republican, is part of a long-term legislative effort by the anti-abortion movement to gut Roe v. Wade and severely curtail abortion access nationwide.

Twenty-week abortion bans, enacted in more than a dozen states and struck down in two, violate the Supreme Court’s standard that abortion can be restricted only when a fetus is viable outside the womb. Many, including the one being considered by the Senate, are based on claims not supported by most scientists about when a fetus feels pain.

Only about 1 percent of women seeking abortions do so after 21 weeks, and they often make that decision because a fetal abnormality has been found or because their own health is in danger. Twenty-week bans particularly curb access for poor women, who often struggle to find the money and time for the procedure.

The Senate bill contains exceptions for rape and incest if the women reported the abuse to law enforcement and sought counseling 48 hours before the abortion. But there is no exception to protect the health of the pregnant woman.

Abortion providers, who already face harassment and threats to their lives and work, would face criminal penalties, with a sentence of up to five years, for performing abortions after 20 weeks. The locations of all such procedures would need to be reported to the federal government.

Though President Trump urged Congress to “pass this important law and send it to my desk for signing” in his address to the anti-abortion March for Life this month, Republicans are almost certain to fall short of the 60 votes needed to formally take up the bill.

Still, abortion rights advocates and medical professionals are taking the legislation seriously, since abortion foes are working hard for it. The prospects for such a ban considerably diminish if the Democrats take back either house of Congress after the 2018 midterm elections. And if they control the Senate, Mr. Trump will have virtually no chance of picking another anti-abortion Supreme Court justice.

Since announcing his candidacy, Mr. Trump, at one time a supporter of abortion rights, has embraced anti-abortion politics with zeal. But that seems to be a matter of maintaining evangelical support. His concern for fetal life cannot be fairly measured, but his sensitivity to the needs of women, or lack of it, is well known.

Some sponsors of the version of this bill that the House passed in October seem to share Mr. Trump’s attitude. One, Trent Franks, Republican of Arizona, resigned his seat in December after it was reported that a female staff member had felt pressured to have sex with him as part of a surrogacy scheme. Another, Tim Murphy, a Pennsylvania Republican, voted for the bill just hours after news broke that he was accused of pressuring his mistress to — get this — have an abortion. He later quit.

Ultimately, the fate of the ban and other anti-abortion measures will be in the hands of voters. For supporters of abortion rights, the choice should be clear.