How is that a fair or even interesting comparison, though? Islamist terrorists aren't killing people ostensibly engaged in criminal acts. Islamist terrorists aren't otherwise expected to be agents of the government charged with using physical force to protect the laws. Islamist terrorists target innocents in a deliberate effort to maximize damage and loss of life. Body counts tell almost nothing of the story in an honest comparison of the threat from police officers vs Islamic terrorists.
US citizens are at greater risk of far right or Christian extremists than they are of Islamist extremists
This is a slightly more interesting comparison, but even then you have to look at who the FBI and other law enforcement agencies are watching to understand that Christian extremists are individual actors who target specifics like abortion providers. They're not looking to take down all of Western society. They aren't amassing armies in other countries to assert 6th century law on all the territories that they conquer.
So sure, Christian terrorists' kill numbers might be comparable or even greater than Islamic terrorists domestically (if you unfairly exclude 9/11) - but that doesn't mean that they're the same level of threat in a strategic geopolitical sense.