Roberts, as the head of the federal judiciary, has been facing mounting pressure to protect the courts from political interference. With a lifetime appointment, it remains to be seen whether the 70-year-old Chief Justice will take further steps to defend judicial independence as Trump continues his broadsides against the judiciary.

The chief justice is "trying to explain to the people of this country how the legal system works," retired Supreme Court Justice Stephen Breyer said.

Chief Justice John Roberts' rebuke of President Donald Trump's call to impeach a judge marks a growing showdown between Trump and the courts.