Because Trump may do exactly what he did! This is why they really fear Trump.
“Think about what four years of a retribution presidency might look like. He could order the investigation and prosecution of individuals who he sees as enemies, I’m sure I’m on the enemies list, because the president, constitutionally, does oversee the Executive Branch entirely, which includes the Department of Justice, prosecutors and investigators. So he could commission direct that individuals be pursued. He could also direct all kinds of other conduct that people would maybe taken to courts to try to stop but who enforces court orders? Mostly of the United States Marshal Service, which is in part of the Executive Branch, and reports to the president,” Comey said, before warning Trump would “destroy” the country.
“Think about what four years of a retribution presidency might look like. He could order the investigation and prosecution of individuals who he sees as enemies, I’m sure I’m on the enemies list, because the president, constitutionally, does oversee the Executive Branch entirely, which includes the Department of Justice, prosecutors and investigators. So he could commission direct that individuals be pursued. He could also direct all kinds of other conduct that people would maybe taken to courts to try to stop but who enforces court orders? Mostly of the United States Marshal Service, which is in part of the Executive Branch, and reports to the president,” Comey said, before warning Trump would “destroy” the country.