"making his way out of the White House through a secret tunnel"
Right, because there is a tunnel in the White House that the Secret Service doesn't know about/hasn't bugged and rigged full of detectors nor have a pair of Marines posted at either end.
I'm all for suspension of belief, but it has to be at least plausible. Give me a traffic jam and a sudden, inspired escape, and I'll go along because, even if dubious, it just might happen.
But a secret tunnel, unknown to an organisation who has been in charge of the White House for almost as long as there have been Presidents ? And this one new guy who has only been there for, at best, three to seven years, knows about it ?
Well that just about sums it up : I'll keep on reading Tom Clancy novels. When he pulls a Deus Ex Machina out of thin air, he's good enough to at least dress it up properly.