Amy Howe at SCOTUSBLOG points to a footnote in the Roberts opinion:

We agree that Presidents are neither absolutely immune from state criminal subpoenas nor insulated by a heightened need standard.” Here’s some key language: “We agree that Presidents may challenge specific subpoenas as impeding their Article II functions.” “And although we affirm while Justice Thomas would vacate, we agree that this case will be remanded to the District Court.”

Trump’s facing prosecution the moment he leaves office on state tax fraud charges.