Die Hard on a White House.
That’s basically it right there. You have your former law enforcer — here his name is Mike Banning (Gerard Butler) and he used to be Secret Service assigned to protect the President (Aaron Eckhart). During a snowstorm, Some Damn Thing hit the Presidential Limo’s windshield and fishtailed the car nearly off a bridge. Banning was able to save the President, but not his wife, and since the President can’t stand to be reminded of that night, he has Banning reassigned.
Okay, then you have your terrorists commandeering a building — here they attack the White House in a cargo plane the same day the President (whose name is Benjamin Asher, and whom I’ll be referring to as Asher for the remainder of this), Vice President, and Secretary of State are meeting with the South Korean Prime Minister.
As the gang retreats to the Presidential Bunker, one of the PM’s aides reveals himself as Kang Yeonsak (Rick Yune), a North Korean terrorist with a backstory that blah, blah, blah. He shoots a lot of people in the head and wants to blow up things. That’s all we need to know.
You have your former law-enforcer invading the building — in this case, Banning storms the White House after Kang’s goons take out every Secret Service man and Marine on the premises.