So what is the Overton Window? The theory is named after Joseph Overton, a former vice president of Michigan's Mackinac Center. The Goldwater Institute explains the theory:
"The Overton Window" is set to be released June 15. Meanwhile, the Left is already bashing it, despite rave reviews from authors such as Vince Flynn (love him!), Brad Meltzer and Nelson DeMille.The theory states that policy proposals in any given area can be arranged from the most freedom to the least free. But only a narrow window of those policy options is considered politically acceptable to politicians. This smaller list of policy options does not necessarily reflect the stance a lawmaker would prefer to take on an issue. Rather, this “window” looks onto the range of choices the lawmaker believes he or she can support and still win re-election. As ideas change in society, the window shifts to include new policies or exclude old ones.
PS--the poem featured in Beck's trailer is this one by Rudyard Kipling, despite folks on the Left claiming that each "over-the-top-line" was written by Beck himself.