Fuck this: Secret Service messes up and we pay the price? No way.

[jberryhill]

30. Here's the thing about that

The reason that we used to send aircraft toward Russia and the reason Russia still sends aircraft toward our defense zones is to watch the tracking radar systems light up, and thus gain valuable information about the defense systems with an eye toward penetrating them.

In order to counter that type of testing, you want to act "within" the limits of the system. If the severity of a threat can be assessed as it approaches, then it is preferable not to demonstrate the outside limits of the effectiveness of the defensive system, to avoid having the capabilities of the defensive system fully exposed.

The situation here is that the President and his family were not on the premises. If he had already been confidently flagged as "unarmed nutter" mid-sprint, then grabbing him at the door is preferable to "demonstrate hidden death ray device on roof".