The president lies.
Example: He said during the campaign that Hillary Clinton was the founder of ISIS. We knew then and now that she is in no sense the founder of ISIS.
I have a relative who lies the way Trump lies. He knows he's lying. He knows I know he's lying. He knows I know it isn't worth the trouble to engage him on the lie. I have no idea why he does this, and I don't care.
The things that Trump lied about during the campaign weren't consequential. Everyone knew that Hillary Clinton wasn't the founder of ISIS. He kept saying it. Shrug.
He lies about things that are consequential now. And they are escalating. It's as if he's testing the water, to see what happens. If nothing happens, he will keep escalating until he hits some kind of limit.
His staff, while they haven't exactly said he's lying, they call it joking, or they explain that you can't take him literally, or that he has alternate facts. These are all ways of avoiding saying the words. But the net-net is they are telling us that he lies.
So we know that he lies. Pretty much everything he says is a lie. I can't recall him saying anything that wasn't a lie.
We are always deciding if this is acceptable. You can say that the Republicans in Congress will never do anything, but the fact remains that given our form of government, which is well-specified, the fact is that we accept, up till now, that our leader lies.
At some point presumably we will decide this is not acceptable.