It’s stupid to think that the Smithsonian cannot reject a submission.
But since the Smithsonian is creating exhibits that carry credibility based on being managed by the govt (tax dollars), it’s appropriate to ask who is in control of the narrative.
From the article: Judge Trevor McFadden, from the District Court, declared that the actions of Kim Sajet, the Director of the Smithsonian National Portrait Gallery, were ‘insulting, partisan and odious’,
I think they can reject anything with “good” reason but not for political bias. (the question becomes, what is “good reason”?)