Well it's for a timeline I'm writing where fascism rises in America due to a combination of multiple factors. Basically the premise is that Abraham Lincoln becomes convinced of nativism in the 1840s and also develops a revanchist hatred for Southerners, which leads to him having a near-fanatical devotion to the Union. During the chaos of an alternate Civil War (which isn't a proper civil war but more of a series of terrorist attacks carried out by the Knights of the Golden Circle), Lincoln begins curtailing some political freedoms. He then raises a Union army, which like OTL, happens to be the largest standing army in the world With this powerful tool at his disposal, he, William Seward, General Grant, and General Sherman conspire to overthrow the US government. Lincoln is set up as dictator, and after delivering a resounding victory against the Southerners (along with their Indian and French allies), Lincoln's dictatorship is justified in the eyes of the people, and he legitimizes it through a new constitution and political party, thus creating an official fascist government. Stephen A. Douglas, George McClellan, and Robert E. Lee are killed in political purges. Lincoln rules until his death in the 1890s and I haven't really thought through what happens next.
Anyways, I was thinking that this new fascist America would probably keep the same flag (as the US still remains a federal republic).