A U.S. Postal Service official has alleged that the agency is moving forward with a “secretive, rushed” effort to implement President Trump’s order exerting federal control over mail voting, despite a court order blocking those plans.

The official filed a whistle-blower report, published on Tuesday morning by the office of Senator Richard Blumenthal, Democrat of Connecticut, asserting that the “risky and haphazard” implementation of Mr. Trump’s order could lead to a “catastrophic failure” in the mail ballot system ahead of this year’s midterm elections. The report said that the agency had planned to complete the new digital system overseeing mail ballots by Sept. 1.

“Potentially millions of American voters may not receive their mail-in ballot this election cycle in a timely manner, or at all,” the official said in the report, which was prepared with the assistance of Whistleblower Aid, a nonprofit group that represents people seeking to expose potential lawbreaking.

Speaking to reporters by phone on Monday, Mr. Blumenthal said of the report that “the main takeaway for me is that the Postal Service has designed a system to disenfranchise millions of Americans. One-third of all Americans cast their ballots by mail, and the U.S.P.S. puts all of their votes at risk.”

A Postal Service official declined to comment on the record.

Voting by mail will become much more difficult, if not impossible, for tens of millions of Americans if the Postal Service is allowed to implement the restrictive rules governing mail voting that Mr. Trump has demanded.

Mr. Trump has repeatedly promoted false claims of widespread fraud through mail-in voting, which he has described as “cheating,” “corrupt” and “horrible,” even though he voted by mail in two elections this year. He has moved to restrict mail-in voting using a variety of procedural and legislative levers.

Those moves have led to a pileup of legal rulings and challenges surrounding the nation’s electoral system just two months before the midterm elections. The rules could especially affect states where some of the most competitive races for House, Senate and governor will determine control of Congress and state governments.

Michigan, where 37 percent of votes were cast by mail in 2022, would be one, with competitive statewide contests and multiple battleground House races. California, which mails ballots to all voters, is expected to be central to Democratic efforts to win control in the House.

The Supreme Court had allowed the Trump administration to move ahead with Mr. Trump’s mail ballot executive order, reasoning that a lawsuit challenging the order was premature because the administration had not started implementing its plans.

But days before the court ruled, the Postal Service formally published a new plan to comply with the executive order. Judge Indira Talwani, a Federal District Court judge in Massachusetts, reasoned that the stakes had changed with the new plan and temporarily blocked it, concluding that the agency’s plan appeared to overstep its legal mandate and could spark chaos by changing rules a little more than two months before an election.

The whistle-blower report provided specific details of the Postal Service’s effort to rapidly implement a new digital system for mail ballots, even as a federal appeals court had blocked the plan before the Supreme Court intervened. Work has also continued on the system even after Judge Talwani ordered the plan halted last week, the report said.

The official at the Postal Service raised “grave concerns” in the report that the verification process in the system could reject tens of thousands of ballots in a bulk-mailing batch if “even one bar code on one single ballot” failed to properly scan, and that the rushed, “slapdash” development of the system would significantly increase the chance of errors and other failures in the verification process.

The Department of Homeland Security (DHS) has published a new webpage that will help carry out President Donald Trump’s plans to create a national voter registry and shape who can vote in the upcoming midterm elections.

It’s the latest sign that the administration is hurtling forward with plans to put Trump’s dangerous anti-voting March executive order into effect.

The order directed DHS and the Social Security Administration (SSA) to centralize data from across the federal government to create lists of eligible voters in all 50 states.

The new website, dubbed the “State Citizenship Lists Portal,” claims the lists are “coming soon.”

According to a memo it released in June, DHS plans to have the portal fully functional by Friday, Sept. 4.

Voting experts have said the federal government lacks the authority to create such lists, which could be used to challenge voters’ inclusion on state registration lists, and therefore their right to vote.

Combined, the lists sought by Trump would amount to a nationwide voter eligibility database managed by the federal government. No such thing has ever before existed because the U.S. election system is designed to be managed by states and localities, not the executive branch.

Privacy experts have also warned that the Trump administration would likely violate privacy laws in centralizing Americans’ personal data to compile the lists.

On Tuesday, the Electronic Privacy Information Center (EPIC), a privacy advocacy nonprofit, filed a lawsuit against DHS and SSA, challenging the effort as an unconstitutional attempt to seize control of elections.

“No statute authorizes Defendants to share and centralize vast volumes of Americans’ sensitive personal data across government agencies to create and disclose the ‘State Citizenship Lists,’” the lawsuit, filed in federal court in Maryland, reads.