I was wondering if there was any way to get Kimball to arrive at the dam if you are hostile with the NCR and the Legion, and have already failed Don't Tread on the Bear and Beware the Wrath of Caesar. I can't think of any way myself, but I was wondering if I have missed something. I always wait until after Kimball visits before I turn both the NCR and Legion hostile, but LR caused me break my rule.

My guess is that he won't come because with me as a danger, the NCR has determined that the president's visit would be too big of a security risk, so they cancelled it. But the option to save Kimball is still active in my Wild Card: Finishing Touches tasks menu, so I'm thinking that it might be possible.