I have run the scenario several times and each time the prez gets nailed by a sniper. Anyone know where that sniper is?

I usually hang out on the launch pad and disarm the vertibird and then tell Ranger Ryan or whatever his name is about the bomb on the vertibird. Just say by the vertibird and watch the engineer do his thing. With high science or repair you can get the bomb off the vertibird, with a high sneak you can get the detonater off of the engineer. Anything that interrupts their plan usually ends up with the president getting away. Well... unless you leave the bomb alone and only get the sniper.... but you get the idea

The sniper is on the building behind the launch pad. Keep looking at the soldier stationed there, and you should see an event happen that shows when the sniper shows up.

The sniper is in the tower opposite to the one the vertibird goes if you look you see a guy kill aranger there easier option examine the vertibird and tell the ranger there bomb then the sniper is killed by NCR.

Just stand up there in the tower with a companion. Your companion will probably nail the guy before you realise whats going on. Once thats done, you can worry about the other assasination attempt...

Companions do not kill the imposter the ncr do or you have to kill him boone never noticed him I killed him then disarmed the vertibird

Thank you all so much for the prompt responses ... now I can put the rum away so this stuff won't drive me to drinking. LOL