Zangara succeeds and assassinates FDR. Garner refuses deficit spending or building up the military. Huey Long stokes lower class rage in his drive for power. Garner is harsher in his attacks on unions. This leads to a militarized response by strikers which leads to riots throughout the country. The 1936 election is grim as no one has answers. Garner and Long spar as Landon meanders.
The American economy muddles through as WWII begins. France falls, Churchill struggles to bolster morale without American aid (America will sell, but not give away support). The 1940 election brings even greater anger as Long wins the Democratic nomination to great fanfare but is assassinated, many say by big business. Riots worsen across the country. Lindbergh argues for focus at home rather than abroad.
As Germany turns it's might against the Soviets, America roils. The Japanese rampage across China and the president decides to take economic action. Many Americans see it as a means to distract Americans by an illegitimate president, reward war profiteers and send sons to die beyond the horizon. Riots increase.
Japan attacks Pearl Harbor embroiling them in a war with the US. With the US Navy suffering from the Garner years, it proves vulnerable to Japanese attacks. The loss at Midway incenses the American public as it sees nothing but losses as well as the realization Japan will control the Pacific until at least 1943.
The Soviets finally collapse in 1943. The UK, struggling financially, sue for an armistice. The US gives way to a stronger federal government to curb the violence and drive the nation to victory. The Germans watch while digesting it's spoils.
With the rift between the UK and America, the former does not aid or inspire the latter to research the atomic bomb. This turns the war in the Pacific into a Savage, near genocidal affair. By 1947, the US invades the home islands. The losses are so monstrous that the nation comes unhinged. The military, having lost so much, sacrificed so much, dealing with increasingly inept administrations and forced to even fire on American citizens, finally turn against the American government. Americans having suffered nigh on two decades, desensitized by poverty, war, and betrayal, accustomed to an increasingly authoritarian government and desperate for stability readily accept the new regime. Japan is finally broken in a cruel war by 1949. America, under a martial regime, rebuilds preparing for the threat waiting just past the Atlantic knowing the price of doing nothing.