From day one Trump's claim was preposterous on its face, both for lack of evidence and for misstatement of anything the President has the power to do. When people make preposterous, evidence-less claims, we usually do and should call them nonsense and lies. As I noted a couple weeks ago, President Trump is - via his office - literally the owner of all possible evidence that something like this happened. If something like this is true, he can show us the evidence. He can show Congress the evidence.
Now we've gone to the ridiculous lengths of having actual congressional investigations. And the representatives of the President's party in Congress have said there is no evidence that this happened. They are of course hanging on this 'no evidence' locution to avoid the discomfort of calling their party's leader a liar. The press shouldn't share that loyalty.
In any other context, when we have a claim that it wildly improbable verging on impossible on its face, when no evidence is provided and when outside investigations say there is definitively no evidence whatsoever, we calls those claims lies. Or the rantings of an unhinged person if we want to grant some accommodation for mental incapacity. If someone says aliens landed in their backyard and has a similar lack of any evidence whatsoever, we call that person a liar or a crazy person. We say it's not true. Full stop.
As we know, by definition, you cannot prove a negative. You can only show there is no evidence whatsoever to support the claim. But this isn't a seminar on philosophy and empiricism. We call these lies.
This is classic enabling behavior. It is amazing, crazy that we've actually spent two weeks discussing this as a real issue. Now, because of this enabling, we have a bona-fide, if minor, international incident with the US's closest ally, the United Kingdom because the President's press secretary actually spread the accusation that the UK somehow conspired with President Obama to do this. That's nuts. Nuts on its own terms but even more nuts that this charade has spread to this level.
The President had a moment of anger, desperation, agitation and made this farcical claim. Admittedly, we don't have a lot of experience flatly rejecting a public accusation from a sitting President. But it's a new world. Treat it as such.