AMERICAN politics has a new rhythm: the president does something outrageous; lawsuits fly; a judge stops the new policy in its tracks. The ban on travel from Muslim countries came first, halted within hours of its appearance at the end of January. The second and third versions of the travel ban have been frozen too, though version 2.0 escaped full Supreme Court review when it expired earlier this month. The White House’s attempts to punish sanctuary cities for refusing to cooperate on immigration enforcement have also been halted by federal judges—three times. Now Donald Trump’s ban on transgender troops—a policy he announced in a series of tweets over the summer—has been dealt a significant legal blow.

On July 26th, Mr Trump tweeted that the government will no longer “accept or allow transgender individuals to serve in any capacity in the US military”. Why this reversal of an Obama-era policy opening the armed services to transgender people? “Our military must be focused on decisive and overwhelming victory”, Mr Trump explained, “and cannot be burdened with the tremendous medical costs and disruption that transgender [sic] in the military would entail”.

The trio of tweets evolved into a presidential memorandum on August 25th barring transgender people from entering the military and setting March 23rd as the deadline by which the military would authorise transgender people already serving to be let go. Several lawsuits sprang up challenging the constitutionality of Mr Trump’s discriminatory move toward thousands of current and future transgender soldiers. On October 30th, Colleen Kollar-Kottely, a 74-year-old federal judge first appointed to the bench in 1984 by Ronald Reagan—and sitting since 2007 on the federal district court for the District of Columbia—issued a temporary injunction striking at the heart of Mr Trump’s ban.

Judge Kollar-Kottely began her 76-page opinion by noting that many of the plaintiffs, “current and aspiring service members who are transgender”, have completed tours in Iraq and Afghanistan and have served “with distinction” for years or decades. Mr Trump’s ban on trans troops inspires fear in these individuals of “devastating impacts on their careers and their families”. The plaintiffs stand to lose their livelihoods and health insurance for themselves and their families—not to mention their dignity. One plaintiff who “loves this country and [has] served it faithfully and well” for 14 years, Judge Kollar-Kottely wrote, resents the change in policy. It is a “terrible blow” to the woman, she wrote, “to be told that [she is] no longer worthy to serve”. All she asks is “to be allowed to serve [her] country and to be evaluated based on [her] job performance rather than on [her] status as a transgender person”.

The constitutional case against Mr Trump’s ban begins with the equal protection of the laws, the principle that affords vulnerable groups special protection against official mistreatment. The equal-protection clause is found in the 14th amendment, which applies against the states, but the Supreme Court has for some time read it to apply against the federal government, too, through the Fifth Amendment's due-process guarantee. Judge Kollar-Kottely explained why transgender people qualify as a “suspect class”, a group deserving of special judicial solicitude. Transgender individuals have “been subjected to unique disabilities on the basis of stereotyped characteristics not truly indicative of their abilities”, she wrote, citing Supreme Court precedents. According to one study, over three-quarters of transgender students report being harassed in school. And transgender people “have immutable and distinguishing characteristics that make them a discernible class”, another requirement for heightened protection.

In light of the marginalised status of transgender people in America, and the gender discrimination behind their exclusion from the military, the government must show an “exceedingly persuasive justification” for treating them differently, Judge Kollar-Kottely wrote. Here, she observed, the administration failed miserably. The reasons on offer—medical conditions affecting deployability, higher health-care costs and threats to “unit cohesion”—“do not appear to be supported by any facts”. After considering each argument in turn, the judge found “absolutely no support for the claim that the ongoing service of transgender people would have any negative effect[] on the military at all”. To the contrary, “there is considerable evidence that it is the discharge and banning of such individuals that would have such effects”. Given all that, since the plaintiffs are “likely to succeed” in their effort to strike down the ban as unconstitutional, Judge Kollar-Kottely agreed to block most of the order, for now. She left in place only Mr Trump’s ban on funding for sex-reassignment surgeries, as none of the plaintiffs persuaded her that this prohibition would affect them personally.

Like many of the rulings freezing Mr Trump’s policies, Judge Kollar-Kottely’s injunction is temporary, pending full judicial consideration, and will likely be appealed. The Department of Justice says it disagrees with the ruling and is “currently evaluating the next steps”. It’s a familiar bind for a White House that seems bent on testing the bounds of America’s constitutional norms.