Falling Skies season 3 picked up seven months after Cochise - a leader from the alien race Volm - landed in Charleston. While the show's world hasn't changed, the time jump introduced in "On Thin Ice" allowed for advancement and a bigger picture of the story.
Tom Mason has been elected President and leader of Charleston. However, Tom just wants to be known as Tom and not called President. He refuses to sit in an office to lead and instead continues to go out on missions and fight against the aliens. He's remained true to himself and the cause.