Enclave#
1. Set off the nuke on the Presidential level#
You must have the Presidential Access Key and the red keycard from a scientist on the reactor level (the one with the Enclave soldier right next to him). When you have both keys, use the control panel next to the bomb.
There doesn't seem to be a way to successfully set the bomb, it always blows up in 5 seconds. Save your game before you mess with the nuke!
"Bomb has been activated and will detonate in T-minus 5 min . . Error in countdown procedure. Countdown restarted at T-minus 5 seconds. Please make sure you are at least 80 miles from the blast area. Have a great day."