I'd like to give you a chance to show me what significance Trump's 'lying' has had - after all if he is deliberately lying, it has to be for a purpose, or alternatively start to reflect on whether he has been unfairly denigrated.
Since we can not see in his mind, we can never say what the purpose of any lie is, we can speculate, but we can never be sure.
Are his lies deliberate? sometimes they are, but also here we can never know for sure.
But as i said before, the alternative could be even worse, he could tell lies out of pure stupidity.
So i think to the best way to know whether he is a liar, is simply looking if the statements he makes are true or not.
For instance, if he says his inauguration drew the largest crowd, and it is demonstrably wrong, he is a liar.
I don't care why he lied about, if it is not true it is a lie.
Granted, maybe not the worst, but it is a bit symbolic, it is the one that set the tone for his whole presidency.
Now if can you cannot debunk this without resorting to whataboutisms, conspiracy theories, appeal to leftist propaganda, or moving the goalpost about what is a actually a lie, then trump is logically a liar.