Time Leap Future Imperfect

World War 3 has hit America in 2019. Turning a bright and prosperous country into a desolate location. However what the Islamic Coalition don't realize is that even though they now rule, Americans are still patriotic and determined to undermine the enemy anyway they can. One of their worst headaches is the leader of the Washington Rebel group. She leads ex-US military against the enemy. She is a young scientific genius, who was in the Pentagon when the war started. On her own she designed a Time Watch that could send her forwards or back in time for a few hours. One day she went back to 2017 to get supplies and was intercepted by Pentagon Security just as she was about to leave to go back to her own time. Unfortunately one of them grabbed her arm and he ended up in her future and is unable to return back to his own time. Except for short trips. He stays to help her against the enemy and reunites with old military friends who join up with them to form the Washington Rebels. Their base is the Pentagon nucleus which is impregnable to the outside world.