It just doesn't make sense to say that all politicians lie equally. Trump is in a league of his own and he has worked diligently for that accomplishment.
I really don't think that he is.
Obama, for example, lied very eloquently and professionally and always gave himself an out with how he constructed his statements. PolitiFact, which conservatives are now trying to whitewash as a liberally-biased site, said that Obama's oft-repeated "if you like your plan you can keep it" claim was the "Lie of the Year" in 2013.
IMO, Obama was able to get away with a statement like that (relatively speaking) because there isn't anything written in black and white in the law that removes access to a specific plan or doctor. However, when he was making that statement, Obama knew that the law would institute certain minimum coverage standards and he knew that millions had those plans, so he knew that some people would not be able to keep that plan. If they couldn't keep the plan, then they potentially couldn't keep the same doctor. Obama knew that full well, but it didn't keep him from saying that every day.
In contrast, Donald just goes on Twitter and says "Obama put a phone tapp on me" without any evidence.
He just does it more brazenly than other politicians, and of course the media is more eager to cover his lies than they are with Obama.