Okay, keeping it short: the Democratic Party is lying about being pro-defense.
At least those in the current leadership. I can find plenty of pro-defense Democrats in the rank and file, even among politicians.
To take your swimming analogy, if swimming must be done, I would rather it be by someone who knows how to swim, has done it before, and isn't worried about the cold. Not someone who will do it half-assed and jump out of the water at the first opportunity, whether or not the job is done.
Okay?