Except, he said he had "nothing to do with Russia" less than a year after negotiations had stopped on the tower, while in the same breath naming some stuff he had done from 2013 in Russia. Not a lie by commission, but one by omission. Why leave out that he had made attempts to develop real estate in Russia? There is a moral obligation to disclose relevant information in good-faith conversation, and that obligation is especially acute when you're running for President of the United States. Trump's statement that he had "nothing to do with Russia" is a lie by omission, and given the usual obligations in conversation, that Trump would omit this fact is troubling. It adds to the various connections his campaign staffers and advisors, friends, and family have with Russia, and those, in light of the fact that the Russians are known to have attempted to influence our elections, are even more troubling.
That is one problem--others have been pointed out by contributors to this thread.