Amidst all the papal hubbub, you may not have heard that an important piece of legislation died in the Senate this week. It's bound to be resurrected in the coming weeks and months. But for now Senate Democrats have succeeded in blocking the Pain-Capable Unborn Child Protection Act, which would ban all abortions after 20 weeks (with exceptions for rape, incest, and the life of the mother).

This was a big mistake for both American liberalism and the Democratic Party — one that they will soon come to regret.

The reasons are both political and moral.

Flush from their sweeping victory in the fight for same-sex marriage, many liberals may be inclined to think things are going their way on every issue in the culture war. But that simply isn't true about abortion. Yes, exactly half of the country calls itself "pro-choice," but when pollsters ask people their views broken down by trimester, the results look far more conflicted. While 61 percent think abortion should be legal during the first trimester (up to 12 weeks), that number drops all the way down to 27 percent during the second trimester (13-27 weeks), and it collapses to 14 percent (with a whopping 80 percent of Americans thinking the procedure should be illegal) during the third trimester (27-40 weeks).

Those are stunning numbers, suggesting profound ambivalence about the morality of terminating a pregnancy. And the numbers are only going to get worse, as ultrasound technology improves and medical advances slowly move the age of viability closer to conception. Mark my words: Sooner or later, and probably sooner, Democrats are going to pay a price for defending an unreasonably maximal position on abortion. Much better to fall back to a defensible position now than lose a battle more decisively down the road.

This is especially so when the Pain-Capable Act would merely bring the United States into conformity with the way abortion is treated throughout most of the world — including in that notorious backwater of oppression for women, Europe. The fact is that just six other nations in the world — and just one member of the EU (The Netherlands) — permit abortion-on-demand after 20 weeks. Aside from The Netherlands and Canada, the U.S. stands shoulder-to-shoulder with China, North Korea, Singapore, and Vietnam on this issue.

But wait, cry the pro-choice activists: Abortion is a fundamental right! We don't base rights on domestic opinion polls, let alone on what other countries do. Rights are absolute. They're supposed to protect people against the tyranny of the majority.

That's exactly right. There's only one problem: As just about everyone who isn't a pro-choice activist understands, abortion pits the rights-claims of two human beings against each other — the liberty of the pregnant woman and the life of the baby she's carrying. Normally one person's right to life would override another person's right to express her liberty by killing that person. But there are of course two complicating factors in the case of abortion that make it a uniquely difficult moral challenge to adjudicate. For one thing, one of the human beings resides within the other human being's body. For another, the moral status of the fetus is a matter of dispute.

We know that a baby has intrinsic dignity and rights at the moment of birth. But when it acquires its dignity and rights is unclear, no doubt because the answer is ultimately mysterious. Some say at conception. Others say at implantation. Still others use an inevitably somewhat arbitrary line of demarcation further on in gestation. Viability (the point at which the fetus can survive outside the womb, currently somewhere between 23-27 weeks) is one such line. The point at which the fetus becomes capable of feeling pain is another.

Which brings us back to the Pain-Capable Act.

It's revealing that politicians who oppose the bill tend to deny the medical evidence that the 20-week-old fetus can feel pain. What they don't deny is the underlying premise: that if the fetus does endure excruciating suffering in the act of being killed, it should be protected by law. These politicians no doubt tacitly accept this premise because they have to answer to constituents who might not take kindly to expressions of outright moral indifference to suffering.

That's a real sign of vulnerability for the absolute pro-choice position, which is no doubt one reason why more and more advocates of that position have been staking out increasingly extreme views that do deny the premise — proclaiming the termination of a pregnancy at any stage to be a matter not just of moral indifference but actually a positive good for which no woman should ever feel the least bit of guilt or even ambivalence.

That an activist would operate this way — strong-arming senators to champion views that harmonize with a mere 14 percent of the country — isn't surprising. Planned Parenthood, Emily's List, and their opinion-journalist allies are acting precisely like the NRA and its champions on the right, warning receptive politicians ominously, "Give an inch and the enemy will take more than a mile next time! No compromise allowed!" And so we get no restrictions on late-term abortion, just as we get no serious federal gun control.

What we do get is two more issues transformed into either-or, all-or-nothing wars of attrition — two more issues around which conciliation proves impossible.

In the case of the Pain-Capable Act, this is especially unfortunate. Leading up to this week's cloture vote there was talk of bundling it with another bill providing mandatory paid family leave to make it easier for financially strapped parents to take time off from work to care for a newborn.

I strongly supported both bills. There probably aren't many members of the House or Senate who could say that, just as there probably aren't many who would vote, as I would, both to ban abortion after 20 weeks and to institute a federal pro-contraception program modeled on a recent and very successful experiment in Colorado.

But that's not the point. This is how democratic compromise is supposed to work: not ideological opponents toiling away on a single bill that pleases only the tiny handful of genuine centrists on Capitol Hill, but each side giving the other a good part of what it wants in return for support that makes it possible to get both agendas passed.

Instead, this week both sides got nothing, and the activists were the only ones with anything to cheer about.

That's par for the course in Washington these days. But at least on the issue of abortion, liberals shouldn't kid themselves about their ability to keep it up. Their position is untenable, and time isn't on their side. Those who want to ensure that women keep complete reproductive freedom through the first 20 weeks of pregnancy need to back down on the second 20 weeks. Morality no less than politics demands it.