A federal court denies the government's motion to dismiss the challenge. Wall Street

Last November, a reporter asked House Speaker Nancy Pelosi if it was constitutional for Congress to require Americans to buy health insurance. Ms. Pelosi responded, “Are you serious?”

On Monday, U.S. District Judge Henry Hudson got serious. He denied Health and Human Services Secretary Kathleen Sebelius’s motion to dismiss a lawsuit brought by the state of Virginia challenging the new health law. His ruling stated that it is far from certain Congress has the authority to compel Americans to buy insurance and penalize those who don’t.

Judge Hudson’s ruling paved the way for a trial to begin on October 18, with possible appeals all the way to the Supreme Court, a lengthy process. Some states will likely delay creating insurance exchanges and slow down other costly preparations for ObamaCare until its constitutionality is determined by this case.

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Associated Press
.If mandatory insurance is declared unconstitutional, the entire health law could collapse like a house of cards. Most complex legislation states that if one part of the law is struck down, other parts remain enforceable. But authors of ObamaCare chose to omit that clause, suggesting that the health overhaul won’t work without mandatory insurance.

The law’s defenders say the requirement that everyone purchase health insurance will solve a national problem by reducing the number of uninsured and spreading the cost of care over a larger insurance pool.

Critics say that the requirement tramples the Constitution. Twenty-one states and several individuals are already suing to overturn it. Virginia went one step further, enacting a law that makes it illegal to require any resident to purchase health insurance. The Virginia measure won solid support from both Republican and Democratic state legislators. Despite what Mrs. Pelosi tried to suggest, questioning the constitutionality of ObamaCare is not partisan posturing. A fundamental principle is at stake.

On July 1, before a packed courtroom, attorneys for the state of Virginia argued that if the federal government can require you to buy insurance, it could also force you to buy any product to solve any national problem: a new GM car to bolster Detroit, or stocks to prop up Wall Street.

The Obama administration claimed that the Commerce Clause gives the federal government the authority to mandate coverage. They cited two cases in which the Supreme Court stretched the meaning of interstate commerce like a rubber band. In Wickard v. Filburn (1942), the Court ruled that the federal government could limit how much wheat a farmer can grow to feed his own animals. Similarly, in Gonzalez v. Raich (2005), the Court decided that the federal government could bar a sick person from cultivating a mere six stalks of marijuana. Growing something for personal use doesn’t seem like interstate commerce, said the justices, but individual decisions in the aggregate could have an impact on national markets.

Building on those cases, the Obama administration stretched the meaning of interstate commerce even further, to include an individual’s freedom not to do something—in this case, not to buy insurance. Judge Hudson ruled that “never before has the commerce clause and associated necessary and proper clause been extended this far.”

Ms. Sebelius’s motion to dismiss the case focused almost entirely on why requiring everyone to buy insurance would be good public policy. In other words, the ends justify the means.

Virginia Attorney General Kenneth Cuccinelli, however, made an argument rooted in the Constitution. He cited Alexander Hamilton’s assurances in the Federalist Papers that Congress’s power would be limited and two centuries of Supreme Court cases applying that principle.

In 1993, the Congressional Budget Office said that the mandatory insurance provision in President Bill Clinton’s health plan would be “an unprecedented form of federal action.” In 2009, the Congressional Research Office applied a similar caveat to ObamaCare.

Mr. Cuccinelli argued that Congress ignored these warnings. ObamaCare, he said, was “cobbled together in secret, passed by the Senate largely or totally unread, on a party line vote literally in the dead of night on Christmas Eve.”

Judge Hudson ruled that the court must do what Congress failed to do—apply the Constitution.

Ms. McCaughey is a former lieutenant governor of New York and author of “Obama Health Law: What It Says and How to Overturn It” (Encounter, 2010).