I would add 1) imagining the Civil War as a redemptive arc from the “original sin” of slavery and 2) ignoring the extended brute violence against indigenous peoples that “won the West”
Americans have a difficult time recognizing their country's apparent decline for 2 main reasons:
1. American exceptionalism. Many believe in the unquestionable superiority of the USA and cannot fathom losing the shiny "World's No. 1" crown.
2. Brief yet successful history. The country was cobbled from scratch and became a world power within 200 years. It didn't experience a conspicuous overhaul of its political system.***
Most other civilizations have experienced collapse and, sometimes, renewal, China especially. Americans cannot wrap their heads around collapse because it has never happened to their country (yet). (Also, China's a funny case because remnants of its previous collapse is still hanging out in Taiwan in the form of a rump state.)
*** There's a case to be made that the American political system actually got overhauled into a different beast under FDR's rule. Cornell's political science prof, Theodore Lowi, argued in The End of Liberalism that the US transformed into its 2nd Republic thanks to FDR drastically expanding executive power, laying down welfare state bricks via Social Security, creating various unelected agencies, and more. Interest groups then captured various branches of the government, which means the government no longer represents the will of the people. The country changed from a constitutional republic into "interest group liberalism".