To play devil's advocate, I feel like Melania has been hiding in the shadows trying to protect Baron from the inevitable fallout. To me, it seems like Ivanka is in the real first lady role since we've actually seen her around. Wouldn't be the first time the first lady wasn't the president's spouse.
From what I've seen, it's only happened when the wife has died before the presidency and Buchanan didn't marry.
So it wouldn't be the first time, but it would be for completely different reasons.