See, one of the secret service agents is in league with the terrorists. They're hoping you'll be too exhausted from that first question to ask follow up questions like, "Don't they do background checks on secret service agents?"
Regardless of the convoluted way he gets there, Oldman finds himself in control of the President, his family and more importantly an awesome plane with a kitchen and recliners about 20 minutes into the film.
This would be a pretty sizable bargaining chip in most cases. If we found ourselves with that sort of leverage, it would be about 30 minutes before our demands were met (all four of the mouths on the side of Mt. Rushmore now wrapped around cocks). But in this particular case, the President was only in Moscow in the first place to deliver a speech about how America DOESN'T NEGOTIATE WITH TERRORISTS.
And this just pisses him off more
Oldman seem to be under the impression that America is run by a team of 11-year-olds who only follow official policy until you threaten to hurt someone. Also, and here's where it gets really stupid, Oldman kidnaps the most closely guarded man on the planet in order to negotiate the release of a dictator who's being held by ... Russia. That's right, he's threatening to kill the President of the United States to scare a country that just spent the better part of a century glaring across the Bering Strait and muttering "motherfucker" under its breath.
Why It Failed:
The President turns out to be a total badass and kills all the terrorists. But there's a far simpler reason it fails: they didn't just kidnap the President of Russia. The country that has the guy they're after. The country where Russian terrorists like them would presumably know a few people. The country that, in the '90s, would have probably negotiated the release of a political prisoner for a BMW and a couple of Adidas track suits.