Whenever after December 31, 2011, the President proposes a modification of the force structure for the strategic nuclear weapons delivery systems of the United States, the President shall submit to Congress a report on the modification not less than 180 days before the intended effective date of the modification. The report shall include a description of the manner in which such modification will maintain for the United States a range of strategic nuclear weapons delivery systems appropriate for the current and anticipated threats faced by the United States when compared with the current force structure of strategic nuclear weapons delivery systems.