The U.S. House of Representatives yesterday passed a bill that would ban abortion after five months pregnancy throughout America. It has no legal authority to do so. Regardless of your stance on abortion, if you care about constitutional governance, this should freak you out

Even if "a prohibition on post-20-week abortions would be constitutional if enacted by a state, that does not mean that Congress can enact such a measure," explains The Volokh Conspiracy blogger and Case Western University law professor Jonathan H. Adler.

The federal government, after all, is a government of limited and enumerated powers. Whereas states retain residual police power authority to protect public health and welfare, the federal government has no such authority. Just as there is no constitutional basis upon which Congress could enact a general law against murder, there is no clear constitutional basis for a prohibition or regulation of abortion. As with murder, it's a matter generally left to the states.

Federal legislators' loophole? The Commerce Clause! Of course. This constitutional clause grants Congress the power "to regulate commerce with foreign Nations, and among the several States." The federal government has gotten incredibly good at shoehorning anything it wants to regulate but lacks real authority to into a matter of interstate commerce.

"Congress has authority to extend protection to pain-capable unborn children under the Supreme Court's Commerce Clause precedents," states the new House bill (known as the "Pain Capable Unborn Child Protection Act," or PUCPA). It also claims authority under the equal protection, due process, and enforcement clauses of the Fourteenth Amendment.

"These findings suggest PUCPA's sponsors have at least thought about the constitutional basis for the legislation," writes Adler. "Unfortunately, they have not thought about the question enough, for neither the Commerce Clause nor the 14th Amendment provides authority for this legislation."

"Abortion is not commerce, and not all abortions necessarily occur within the scope of commerce, let alone commerce 'among the several states,'" Adler continues.

As Glenn Reynolds notes, "the performance of an abortion in a local clinic is commerce among the states only if you adopt an unjustifiably expansive reading of the Commerce Clause that supports near-unlimited government power." [emphasis mine] For this reason, conservative Republicans who urge courts to respect the limits on federal power—and who argued the individual mandate exceeded the scope of Congress' Commerce Clause power—should be embarrassed to support the invocation of commerce here. […] The attempt to justify PUCPA under the 14th Amendment is not much better. My friend Ramesh Ponnuru argues that federal abortion regulations are permissible efforts to ensure "equal protection." Writes Ponnuru: "If a state does not offer [equal] protection to persons, Congress may intervene either by forcing states to perform this duty or by stepping in itself." Not really, at least not where protected classes are not involved. Further, remedial legislation under the 14th Amendment must focus on state actors. This is but one of the reasons the Supreme Court struck down portions of the Violence Against Women Act (VAWA) in U.S. v. Morrison, a decision most conservatives cheer. Relevant legal questions—how to define murder, when to excuse the taking of life as defensible or otherwise permissible, even defining what constitutes the end-of-life for medical and other purposes—have always been matters of state law. Drawing such lines necessarily involves drawing distinctions that will please some and offend others, but that hardly creates an equal protection problem, let alone justify federal legislation. Again, where protected classes are not involved, a state's decision to draw different distinctions than would the federal government, even on matters involving life and death, is insufficient to justify a federal law.

For more on PUCPA, here is Reason's Nick Gillespie riffing on Reynolds earlier this week. "Increasingly, mostly Republican state legislatures have been using exactly the sort of onerous, retroactive regulations on medical providers they would decry in any other context to try and shut down abortion clinics in states across the country," wrote Gillespie. "Which is all well and good if stopping abortions at any cost is your goal. But it does come at the cost of pretending that you and your party is absolutely devoted to principle and process rather than results."