Elon Musk may be stepping back from running the so-called Department of Government Efficiency, but his legacy there is already secured. DOGE is assembling a sprawling domestic surveillance system for the Trump administration — the likes of which we have never seen in the United States.

President Trump could soon have the tools to satisfy his many grievances by swiftly locating compromising information about his political opponents or anyone who simply annoys him. The administration has already declared that it plans to comb through tax records to find the addresses of immigrants it is investigating — a plan so morally and legally challenged it prompted several top I.R.S. officials to quit in protest. Some federal workers have also been told that DOGE is using A.I. to sift through their communications to identify people who harbor anti-Musk or -Trump sentiment (and presumably punish or fire them).

What this amounts to is a stunningly fast reversal of our long history of siloing government data to prevent its misuse. In their first 100 days, Mr. Musk and Mr. Trump have knocked down the barriers that were intended to prevent them from creating dossiers on every U.S. resident. Now, they seem to be building a defining feature of many authoritarian regimes: comprehensive files on everyone so they can punish those who protest.

“This is what we were always scared of,” said Kevin Bankston, a longtime civil liberties lawyer and a senior adviser on A.I. governance at the Center for Democracy & Technology, a policy and civil rights organization. “The infrastructure for turnkey totalitarianism is there for an administration willing to break the law.”

Over the past 100 days, DOGE teams have grabbed personal data about U.S. residents from dozens of federal databases and are reportedly merging it all into a master database at the Department of Homeland Security. This month, House Democratic lawmakers reported that a whistle-blower had come forward to reveal that the master database will combine data from federal agencies including the Social Security Administration, the Internal Revenue Service and the Department of Health and Human Services. The whistle-blower also alleged that DOGE workers are filling backpacks with multiple laptops, each one loaded with purloined agency data.