Can you define what a good negotiator is? Who, in your estimation, qualifies as a good negotiator?
I think there are a ton of very negative, but true, statements you could make describing Donald Trump. It seems like he's not a strong reader, he's not very well educated, he's bad at reading a speech. He, unforgivably, seems to believe and actively promote crazy conspiracy theories, including that Obama was born in Kenya. Those are all clear, and I'm just sticking to personal attributes that would describe him without going into politics. The quotes you use to justify your comment all make very strong and from what I can tell accurate descriptions of Trump.
I think it's a stretch to try to say that someone who talked their way into winning a presidential primary and a national election is 'a bad negotiator'. It just doesn't scan.