Featherston won't have nearly as free a hand to do what he wants domestically after a 1921 victory since at an absolute minimum the Senate will be held by the opposition parties. (It's mathematically impossible for the Freedom Party to win the senate that year since they didn't elect any senators before 1921.) Thus Featherston will have to tread lightly on domestic affairs. He can't just start jailing political opponents or ignoring Supreme Court decisions, or he likely gets impeached and removed from office. The Whigs will likewise probably block any public works programs or major tax hikes on the rich that Featherston might try to enact, though they probably will work with him on rearmament and on placing greater restrictions on Confederate blacks.
Featherston will have more freedom to act on foreign affairs and will thus be much more aggressive there. He probably declares an end to Confederate reparations early in his Inaugural Address. President Sinclair probably lets Featherston get away with this since Sinclair didn't like the reparations anyway. Sinclair's decision will be very unpopular with U.S. voters (expect large Democrat gains in the '22 midterms.)
Featherston will likely give greater support to the Imperial faction in the Mexican Civil War and help fund anti-US rebels in Kentucky, Sequoyah, and Houston. Since the Imperial Mexicans won in the original storyline they probably win even faster here since they are getting greater support from the Confederates. Kentucky, Sequoyah, and Houston probably all rise up in rebellion in 1924 after the Canada uprising begins.
Foreign policy is the dominant issue in the 1924 US presidential election with the Democrats nominating a hawkish candidate who promises to crack down on the Confederates. (Lets say Leonard Wood.) U.S. voters, worried about Featherston and angry about the reparations and the loss of Mexico, elect Wood in a close election.
President Wood insists the Confederates resume reparations payments and cease all support for the anti-US rebels. Featherston refuses, and Wood orders US forces to attack the CSA. The Confederate Army is still to weak to really resist US forces, so US troops quickly break through and occupy Richmond and all of Tennessee. Featherston vows to fight on and has General Stuart arrested on charges of treason. The Confederate Army responds by deposing Featherston and establishing a military government which surrenders to the U.S. The CSA is allowed to continue to exist as a nation but has to surrender Tennessee to the United States. The post-Featherston CSA is a mess. The junta is very unpopular for surrendering to the US and is probably facing nasty insurgencies from both the Confederate black population and from Freedom Party diehards.