I’m sure this has been answered here, but I can’t think of good search terms for it.
I wanna say it was Nixon, or near that era. When told by a senior official that resources could be made ready at a minutes notice, he said something along the lines of “Do it now.” They failed and tripled the response time IIRC. Was it Johnson?
Also, hey guys, it’s been a while. 
I heard that it was Carter. The story is not so much that he said “Do it now”, but, rather, that he said “Let’s test this rascal”, with a big fat Fail.
Why would the prez have to do that? The military is kind of known for practicing what they need to do.
Sometimes they do, sometimes they don’t. And sometimes they fail and cover it up. As a former military man himself, I bet Carter knew that.
The story as commonly told is that shortly after his inauguration the relevant security folks promised Carter they could evacuate him from the White House to a safe place on no notice in a very short time. Like in response to a warning of an incoming nuke aimed at DC.
He pulled a no-notice drill & the Keystone Kops routine began.
Or so the story goes. AFAIK, there’s not been a publicly released official investigation into the actual event and the changes made in the aftermath.
Google forth oh Curious One, and report back any primary sources you find.
Hell, drive him home with you.
I don’t know if it’s true or not but the story about Carter ordering a surprise evacuation was mentioned in a Tom Clancy novel. I think it was Executive Orders.
I tried my Googlefu and found that …
… Little Nemo also mentioned this in a similar thread 11 years ago.
That thread was 3rd hit Googling “Carter testd emergency evacuation.” First hit was Chapter VIII of Brackman’s Jimmy Carter Provocateur-in-Chief (pdf).
That guy seems credible.
It’s worth noting that Carter is a Naval Academy graduate and served on nuclear submarines. He’s almost certainly the President who came to office with the most experience about nuclear weapon procedures. So he may have been more aware then most Presidents about the possible gap between how procedures worked in theory (including preplanned drills) and how they worked in real use (including unplanned drills).
Certainly modest.
Alright here’s what I found:
He served on nuclear submarines, but were they fast attack or boomers? Or in nuclear war planning?
He was trained for serving on nuclear submarines as an engineer, but it seems he never actually did before his separation. His at-sea submarine service was all on diesels.
Still, he knew the game.