Timothy Jost is an emeritus professor of law at Washington and Lee University. The opinions expressed in this commentary are solely those of the author.

(CNN) The Affordable Care Act is back in court again. In February, 20 Republican states, led by Texas, filed a lawsuit claiming that when Congress reduced the tax penalty (which most people must pay if they fail to have health insurance) to zero in the 2017 tax bill, it rendered the ACA's individual mandate unconstitutional. Without the mandate, the states maintained, the entire ACA is invalid.

Timothy Jost

In April, the Republican states filed a motion asking Judge Reed O'Connor to enter an order blocking the enforcement of the ACA and all regulations issued under it. In May, California and 16 other Democratic states intervened to defend the ACA. But the Texas lawsuit was so absurd that it garnered little attention.

On June 7, however, the Trump administration's Department of Justice responded to the lawsuit, giving it new credibility. The administration's brief agreed with Texas that the tax bill had made the individual mandate unconstitutional, but contended that unconstitutionality only invalidated the ACA's "guaranteed-issue and community-rating provisions" and not the rest of the ACA. These provisions require that insurers offer coverage to all applicants at the same premium regardless of preexisting conditions.

The Trump administration apparently adopted this position at the last minute, surprising even Republicans in Congress. On Tuesday, Republican Senate Health Committee Chair Lamar Alexander declared, "The Justice Department argument in the Texas case is as far-fetched as any I've ever heard. Congress specifically repealed the individual mandate penalty, but I didn't hear a single senator say that they also thought they were repealing protections for people with pre-existing conditions."

A senior Justice Department attorney on the case resigned last Friday, rather than sign the brief.

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