All politicians lie, what's seemingly different about Trump is the scope and frequency of those lies, and his refusal to admit he even said them given evidence.

Just the refusal to admit them would be bad enough, but since he's gotten away with it just about every time, it shows a worrying trend of there being no accountability. Combined with the frequency, the problem is just multiplied.

I find a politician that can't seem to be held accountable for his actions and that trades on this for more political power very troubling.