Nah, he'd just warn them. In suitably awesome style.
(One night, as George Bush sleeps soundly in the white house...)
(Teddy Roosevelt tumbles through one of the windows. George Bush wakes with a start)
Bush: "AH! Liberals!"
Teddy: "No, you fool! It is me! Your predecessor's ghost from the past come back to give you a teeeerrrible warning!"
Bush: "Umm, you don't look very much like a ghost to me. And is that one of our guard dogs attached to your leg?"
Teddy: (Get off fido!) "Look, it was a metaphor, alright? I'm perfectly corporeal... look, real glass cuts!"
Bush: "Do you need the hospital?"
Teddy: "...maybe later." (sits down) "Now look here sonny, shut up, and listen to my teeerrrrible warning!"
Bush: "Wh...what warning?"
Teddy: "No plane must fly on the 9th of September."
Bush: "But... that's tomorrow!"
Teddy: "Is it? My God!" (looks at calendar) "Oh wait, the mysterious time traveller said it was 2001. You're safe."
Bush: "But if I shut down all the planes and nothing happens, I'll look like an idiot! The economy will lose millions! I'll never be re-elected!"
(Teddy looks in very close and gives Bush a very intimidating glare).
Teddy: "Let me put it this way son, do you want to be remembered as the president who let Al Qaeda fly planes into the twin towers?"
(A few seconds pass. George sweats a little).
Bush: "Umm... probably not?"
Teddy: "Well then you'll clear up this mess good and proper then, won't you? Remember, no planes on 9/11/2001!"
(Teddy jumps out the window, leaving Bush jr looking rather pale).
Bush: "What an awesome guy! I just wish I could've discussed politics, and economics, and we could have discussed my new puppy, and our holiday photo's..."
Teddy: ("Man I dodged a bullet getting out when I did").
(A few seconds later...)
White House Guard: "Sir, I'm going to need to see some ID."
Teddy: (With a bird's nest in his hair from tumbling two stories through a tree) "Can no one recognise me from their history books?! I'm Teddy Roosevelt! I used to live here!"
Guard: "Yep, totally insane. Come with me sir."
Teddy: "Aww shucks."