In the 2013 film "Olympus Has Fallen", North Korean forces take over the White House while the President is meeting with the South Korean Prime Minister.
The Speaker of the House is summoned to the Pentagon situation room, where the director of the Secret Service says the following:
Mr. Speaker... as both the President and the Vice President of the United States are unable to discharge the duties of their offices, I'm officially placing you under Secret Service protection. You are the Acting President of the United States.
Throughout the movie, I saw no mention of the Vice President, and he was not among the hostages.
Where was the Vice President during the movie, and why was he unable to discharge his duties as the President's backup?