Though often used interchangeably, there is a big difference between the pathological and compulsive liar.
There's a general acceptance in the community that politicians don't always tell the truth.
Many are very careful with their choice of words. This is so they can convey one suggestion while using terms that allow them to deny ever saying what you thought they meant.
Believe me, it is somewhat of a political science as I have heard very senior people use the wiggle room as justification for breaking promises that they allegedly never made.