They don't. Their candidates are UNTESTED just like a recipe you haven't tried before.
The proof of the pudding is in the eating.
The recipe may be appealing alluring inviting but only after you take it and taste can you possibly know if the recipe is a good one.
Same with presidential candidates. All they are is TALK. Unless and until they actually are in the job and perform it can anyone KNOW how they will do it.
So it is hope belief opinion only and that ain't worth that much these days. Yet and still so many are so certain that their candidate will do a GREAT job. Amazing.