"Trump made a claim which can neither be substantiated or shown wrong"

So then what is he doing? Telling the truth?

We could debate all day about what a lie is or is not. Fine. 

Then you have to admit at least that what he spoke is unsubstantiated. So when the president makes unsubstantiated claims is that not a cause for alarm? The size of his inauguration crowd is petty – making an accusation that there is widespread voter fraud is NOT. Especially when it is leading to actions such as massive information gathering into a central database and unnecessary calls for voter ID laws. This is just one example.

I have said this before, and it still has bearing if or if not he "lied". I said at it's worse he is a liar - but at the least he is, as you said, making unsubstantiated claims. He is carelessly managing the office of the presidency with wild accusations and mis-truths. Technically lying or not really doesn't change why his statements are an issue.