I don't often make exact predictions about the future; that's not an SF writer's job, and it's really easy to get egg on your face. Howver, here's a prediction:
If Donald Trump is still president, US astronauts will return to circumlunar space around July 16th, 2019 ...
I'm making this a prediction, however, because the POTUS factor.
July 2019 lies within the term in office of Donald Trump (or Mike Pence, depending whether impeachment/removal has happened first then). Trump is nothing if not an egomaniac, and offering him the opportunity to make a historic phone call to lunar orbit in front of the TV cameras is a guaranteed ego-stroke. Trump is of an age to have young-adult memories of Apollo and I can't see the idea not appealing to him if he can take credit for it.
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Quoting Charlie Stross, teller of lies for money and HN user, from http://www.antipope.org/charlie/blog-static/2017/09/bread-an... :