WASHINGTON — The Justice Department issued a withering rebuke on Monday to assertions that a Republican political operative helped draft the department’s request to place a citizenship question on the 2020 census, a decision whose legality the Supreme Court is likely to decide within weeks.

In a brief filed in United States District Court in Manhattan, the department said flatly that the operative, Thomas B. Hofeller, had no role in its request to the Commerce Department in December 2017 for a citizenship question.

“There is no smoking gun here; only smoke and mirrors,” the department’s brief stated. Some supporting evidence filed by plaintiffs in a lawsuit seeking to block the citizenship question “reads more like the product a conspiracy theorist than a careful legal analysis.”

The department’s filing is the latest counterpunch in a lengthy legal battle between the Trump administration and a host of state and local officials and advocacy groups. Those plaintiffs argue that the question is central to a political scheme by the administration to skew census results to the Republican Party’s benefit by reducing the head count of traditionally Democratic slices of the population like immigrants.