Jabs over whether to pressure Justices Clarence Thomas and Samuel Alito to retire could reflect a split between Trump allies and other conservative lawyers.
Some liberals called for Justice Sonia Sotomayor to retire before Donald Trump returns to the White House. But Democrats would struggle to confirm a replacement.
The justices appeared divided over a lawsuit brought by San Francisco over EPA rules for regulating how much sewage the city can send to the Pacific Ocean.
The Biden administration has said its plan would protect communities from pollution and help the nation meet long-term goals to combat the climate crisis.
More than 2 million customers remained without power, 13,000 people were being housed in shelters, and some were threatened by floodwaters that had yet to recede.
A U.S. judge in Texas ruled the Biden administration exceeded its authority in requiring serial numbers, sales records and background checks for ghost guns.