The Titan II missile accident on September 19th 1980 leads to a full-yield 9 MT explosion (which should have been impossible, is probably some sort of fundamental flaw in the arming circuits, and means ALL our W-53 and B-53 warheads need to be taken offline immediately). Thousands dead (including Walter Mondale whose plane was leaving Little Rock that night), millions homeless as groundburst fallout leaves huge exclusion zone across Arkansas/Oklahoma/Kansas. Carter and Reagan both agree to suspend campaigning; Reagan wins but it's a very hollow victory. Severe economic downturn, Pershing II missiles in Europe are right out, and the U.S. is basically headed for another full decade of even worse malaise.
Then on February 20th, 1981, due to heavy fog and pilot error Argentine Airlines flight 342 hits the North Tower of the World Trade Center, leading to a fiery collapse. The South Tower remains standing but is so badly damaged it'll have to be brought down ... somehow (civil engineers have no idea). Until then, Lower Manhattan remains cordoned off.
Then on March 30th, Reagan is shot and killed by John Hinckley (who had some sort of batshit insane plan to marry Jodie Foster and flee the collapse of America together).
God help Acting President George Bush... Meanwhile, absolutely nobody gives a crap about the culture wars at this point. They're worried whether they'll have jobs tomorrow, or get gunned down by a crazy person, or get some sort of radiation poisoning ten years down the road.