That's the problem for him. He could have distanced himself and said, "I wasn't a part of the campaign and I don't know if anyone in that campaign had any contact with the Russians."
But he didn't. He acknowledged (unprompted) that he has been seen as a surrogate for the Trump campaign. Then he said that he had no "communications with the Russians."
He had the opportunity to clarify. He did not. He must answer the questions now.
A lay witness could be forgiven for an incomplete answer. The would-be top lawyer for the US has to know that omitting any valid bases for meeting/communicating with the Russians is not a complete answer.
Maybe he should have clarified, but that is not what was asked of him. Point is they asked him directly about the Trump Campaign and Russia, which he was not working for in an official position and not what he was doing as a high ranking US Senator on the Armed Forces committee.
Why didn't they ask him about the other 25 conversations that he had with ambassadors, including the British, Korean, Japanese, Polish, Indian, Chinese, Canadian, Australian and German ambassadors, in addition to Kislyak?
This is nothing more than a witch hunt led by Warren and Pelosi.