a ball room would be an interesting cover for bunker hardening.

a non critical void space, provides a red herring for penetrating munitions, before they hit actual bunker structure.

germany was doing this with uboat gantries, and munitions factories back in the 40's

That's exactly what the East Wing already was. "...rebuilt in 1942 during the Franklin Roosevelt administration to create more office space and provide cover for a bunker during World War II."

I'm surprised that the building can be easily torn down by an excavator. I would have expected it to be hardened like nuclear facilities.

its whats underneath that really matters.

Specifically: https://en.wikipedia.org/wiki/Presidential_Emergency_Operati...

During 911, the President who was not in Washington at the time was flown to a nuclear bunker:

https://www.wowt.com/2021/09/08/20-years-after-911-look-insi...

It was mostly a facade on that side of the building

He's not demolishing and reconstructing just to leave after 3 years. Saying this as an immigrant who lived under full on military, and pseudo-autocratic democratic rulers.