Author Kate Andersen Brower is shedding some light on the frustrations Michelle Obama felt while she was First Lady ... something the former Prez even admits took a toll on their marriage.
Brower -- who's written several books on The White House -- describes a lunch event Michelle held early in Barack's first term to help launch her Let's Move campaign ... where it didn't turn out the way she hoped.
Kate says Michelle's initiative to fight obesity in America was overshadowed because instead ... the media chose to focus on her offhand comment about her husband quitting smoking.
It was a microcosm of her tenure as First Lady, according to Brower, who says ... despite Michelle's admirable drive to make a difference in the country, she regularly took a backseat to her husband or got tied to gossipy headlines.
The author of "First Women: The Grace and Power of America's Modern First Ladies" says it was frustrating and depressing for a modern woman like Michelle ... something Barack echoes in his upcoming memoir.
As for the current White House ... Kate's an expert on what's going down right now as President Trump's on his way out and Joe Biden's on his way in. Or at least, she's an expert on what NORMALLY goes down during this transition period.
There's nothing normal about this administration though, and Brower believes the usher's office -- responsible for moving First Families -- is having to work covertly.
As we first told you ... the White House residence staff is already walking on eggshells around Trump, and Brower hints it could get a lot worse depending on how Trump and his Chief Usher handle things as Inauguration Day approaches.