They couldn't see that this was fake
Maybe because it was dark or he fired before they could really get a good chance to look at him...
Y'know, the moment they opened the door, bam!
Secondly, y'know how cacs are, obviously, as politicians they live in a wealthy or gated community so the thought process of looking through the peephole, window, etc didn't come to mind since they probably have no fear of opening their door.
All they heard was the words “police” being shouted and they opened up with no hesitation.
It's kinda like how in good/wealthy neighborhoods people sometimes leave their windows unlocked at night, or throughout the day, certain doors are unlocked. That's how serial rapists and murders back in the 70s, 80s, etc used to have a field day commiting their acts of crime in the wealthy middle class neighborhoods because of that naivety thinking crime can't get to them cause of where they reside.