And what do you base this claim on?
True, if a Democrat were to gain power, they would be compelled to make gestures that presented themself as "strong" following a crisis. The key word here is "present." Bill Clinton would talk tough, launch a cruise missile strike, then call it a day.
So what you have is a contrast, gesturing resulting from political opportunism from the Democrats and then genuine strong policy based on principle from the Republicans.
It's not sufficient to play to the cameras.
Do I think they would "willfully" allow an attack. No.
Do I think they would ignorantly pursue policy that would ultimately weaken our security and strength in the world, increasing our vulnerability. Absolutely, and it's been proven by almost EVERY Democrat President we've had this century.
Wilson, Roosevelt, Kennedy, Johnson, Carter, and Clinton. All threatened the security of the world due to their well-intentioned, though totally misguided view of international policy and government.