Immigration activists rally outside the Supreme Court. (J. Scott Applewhite/AP)

The Trump administration asked the Supreme Court on Thursday to deny a request to send a case on a census citizenship question back to a lower court.

In a filing to the court, Solicitor General Noel Francisco said new evidence suggesting links between a deceased Republican redistricting strategist and the government’s decision to add the question to the 2020 Census amounted to a “conspiracy theory” that was “implausible on its face,” and accused plaintiffs of trying to derail the court’s processes at the last minute.

Lawyers for civil rights organizations challenging the decision to add the question had asked the high court this month to put off a ruling on the issue.

They said that if justices were not prepared to affirm lower-court rulings against the question, they should send the issue back to a U.S. district court in New York to consider new allegations that the question was added with the input of the strategist, Thomas Hofeller.

Hofeller wrote a 2015 study showing that adding the question would give an electoral advantage to Republicans and non-Hispanic whites. Documents suggest Hofeller was communicating with the Trump administration over the question in 2017 and earlier with a census official.

But the government filing said the Hofeller study did not show an expression of intent to harm Democrats or minorities and that Hofeller did not, as plaintiffs have claimed, provide the rationale for a 2017 Justice Department request to add the question or influence Commerce Secretary Wilbur Ross’s 2018 memo announcing the question would be added.

The government also questioned why plaintiffs waited until recent weeks to ask a New York judge to issue sanctions over the Hofeller material and to ask the Supreme Court to delay its ruling. Plaintiffs’ lawyers have said they didn’t have the material until May.

In late May, they tried to get the issue before U.S. District Judge Jesse M. Furman of New York, who ruled against the administration in the case now before the Supreme Court, but he said he would not do anything before the high court rules.

The justices heard oral arguments in the case in April and are scheduled to issue a ruling by the end of June. The issue was rushed to the Supreme Court because the Commerce Department said it needs an answer this summer to print census forms.

Robert Barnes contributed to this report.