We literally are always the first line of defense.
If our country survives it is because we care.
Check out the history of WWII and how security concious we were then.
The Civil War had active rebel espionage and sabotage cells. It depended on citizens paying attention to get it rooted out.
Bush and his team calling on us to do the same is imho no less or more than that.
I am sorry that you perceive such a credibility wall that seems to be always too tall to climb over for this President, but it really does seem reasonable to me to point out the obvious: we are the first line of defense.
Ed