I don't see any particular problem with him meeting the ambassador in the first place. There is an issue with his recollection of the meetings, which varies between having no memory of the content of the meetings when that is convenient, and having memories of the content of the meetings when that is convenient. Mighty convenient to recollect things in such a helpful way.
Here his excuse might have been that the patchiness of his memory of what seemed at the time a couple of insignificant meetings with the ambassador meant that he hardly recollected the existence of the meetings but that he is sure he would remember if anything material had been discussed.
Then there's the issue that his testimony gave the appearance of lying. And then his excuse for it, which shows that even when reviewing the question and his answer, he can't see his error or admit to it.
He ought to have known very well the contextual importance of the question. He needed to be candid. He left a false impression. It looks deliberate. If it is deliberate, he perjured himself.
But if he had just said apologetically right away that he understood the question in one context and Franken may have meant it in another, he'd be in a much better position right now.
He's down the bad excuse rabbit hole now and his job above all demands trust. Not a defensible position.
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