Apparently, they get away with it with some of their supporters as can be seen in the comment section of many media. Of course, most of those supporters also know that the Trumps lie even if they don't admit it, but don't seem to care too much if at all: the fact that they think some politicians from the past have lied on occasion (of course, none at the Trump scale, mind you) is enough to make them comfortable with the reality that their President is a hopeless serial liar. Pathetic.