Politicians lie. That's the nature of the game. As sad as it is, many times they either blatantly do it with the intent of just getting elected and doing what they want, or they just simply can't fulfill a campaign promise. At this point, it's just a fact of life.
With that being said, there are some politicians who are bigger liars than others, and to date, Donald Trump could be the biggest of them all.
To compare, the New York Times calculated that Trump told 6 times as many lies in his first 10 months in office as Obama did during his entire 8 year presidency. That's insane.