For two of the most powerful men in the United States, Donald Trump and John Roberts, it has been a delicate dance from the start.

Chief Justice John Roberts pushed back on President Donald Trump’s escalating rhetoric against the federal judiciary on Tuesday in a highly unusual statement that appeared to be aimed at the president’s call to impeach judges who rule against him.

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.