I suspect the president got input from many people for his VP pick. The one thing I hear about the president is that he asks questions, listens to a myriad of opinions, and then makes his own decisions. I have no doubt he listened to Melania, and every other family member, as well as others. Whether or not she was present at the announcement is irrelevant. He made his decision prior to the actual event.
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He better listen to her, she's got super powers!