Nothing alleged about it, Frank. Trump does this too -- he'll go into meetings without key staff any other President would know he needs. An example, which is NOT alleged as I know a few of the people involved -- when Trump met with Putin in Helsinki, he specifically excluded his own U.S. Ambassador to Russia, Jon Huntsman, who was both a subject matter expert, Trump's personal representative to Moscow, and a Russian speaker.
This would be troubling for any President to do, but Trump knows no foreign languages, knows nothing about foreign policy, knows nothing about the world outside of Manhattan real estate, and is brimming with unmerited self-confidence. It's a failure of leadership and ethics on an astonishing level, and undermines his agenda.