I cut such folks some slack.  Believing what President Trump says is a mistake.   Whatever he says is either his gut reaction, (supported only by his emotional bias), or he's manipulating public opinion to improve what he sees as a negotiating position.    Example:   Scream like a banshee so you have room to look generous down the line in negotiation.

In most cases, I think the President speaks with personal bias, not rational judgement or specific purpose.   If a person can't win an argument by thinking rationally, using facts as we know them, I deeply mistrust emotional manipulation.     I've seen it done by both conservative and liberals, but have never seen lying used as a tool in the way that President Trump does.  The man has some serious emotional issues that cause this ultra high need for approval.   He seeks Personal power is a way that I believe to be unhealthy for the nation.