THERE ARE several excellent reasons for exasperation, even outrage, at a poorly defended order by a federal judge last summer halting nearly $1 billion of federal funding just days before it was to be awarded to the Purple Line, a 16-mile light-rail project that would connect Prince George’s and Montgomery counties. However, those reasons do not include baseless allegations that U.S. District Judge Richard J. Leon, whose ruling blocked the project temporarily, and maybe permanently, has a conflict of interest in the case.

Suggestions about Mr. Leon’s supposed bias have been kicking around for a while, more on the rumor mill than in the media — and for a good reason: Whenever journalists examined the allegations, the ethical case against Mr. Leon disintegrated. On the facts, there simply is no conflict of interest.

Unfortunately, those facts did not deter Maryland Gov. Larry Hogan (R), who, evidently frustrated that the Purple Line has remained on hold since Mr. Leon’s ruling last summer, accused the judge of harboring bias and a conflict of interest. The governor suggested that the judge, who was appointed by President George W. Bush, blocked the project because of his wife’s involvement with a group that once opposed it and because of the location of their residence.

The problem with the governor’s assertion is that it is nonsense.

Mr. Hogan blamed the Purple Line impasse on “a judge who lives at Chevy Chase Country Club.” Four problems with that: 1. The judge lives more than a mile from the Chevy Chase Club and two miles from the nearest planned Purple Line station; 2. the Chevy Chase Club has no position on the Purple Line and isn’t directly affected by it; 3. the judge lives three miles from the Columbia Country Club (the club Mr. Hogan apparently had in mind), which has fought the rail line partly because its golf course would be bisected by it; 4. there is no indication the judge belongs to either club.

Then there was Mr. Hogan’s equally scurrilous claim that the judge’s wife “happens to be involved in the opponent group.” In fact, Christine Leon, who has a modest role as a block captain in her neighborhood association, has played no role in a geographically broader community group that did oppose the Purple Line — nearly 10 years ago.

It is fair to criticize Mr. Leon’s slapdash stance, which he is now reviewing. In a flimsy nine-page ruling, he ignored years of study; a Supreme Court opinion that specifically warns against such reversals except when new information “provides a seriously different picture of the environmental landscape”; and the fact that, despite slipping Metro ridership, which might contribute to slightly diminished projections for Purple Line passenger numbers, the light-rail line would still be among the busiest new transit projects in the nation. The judge’s ruling is not unethical; it is merely unfounded.