Is one party a war/aggression deterrent and why?

The classic argument started with Reagan: middle eastern countries withdrew their troops when they heard Reagan got elected because he was such a big scary guy. And ever since then the public has been parroting this sentiment that foreign powers are 'afraid' of what Republicans will do in office. ALSO Democrats are war hawks and Republicans are peace advocates. Can people from either side tell me how this blatant contradiction can be true and how you think of it?