The United States appears to be in uncharted territory these days. Having studied the history of Europe, current events seem more in line with crises in fledging democracies in that continent in the late 19th and early 20th century rather than echoes in American history.
I am thinking in particular of France under the Third Republic and Weimar Germany. (Although I know the second metaphor is fraught with peril.) In both cases the political middle disappeared, and society found itself divided between competing political forces, one that supported a democratic society, and the other willing to compromise democracy in the name of nationalism and the preservation of tradition and its traditional power. For example, in the 1890s, the French Right called their opponents the "Anti-France," and aimed to protect the church and military while attacking Jews and the Left. While they were dealt a defeat during the Dreyfus Affair, they came back in the 1930s and reacted to the Popular Front government of Leon Blum by proclaiming "Better Hitler Than Blum." During the occupation in World War II, they got their wish. I shy away from Weimar metaphors, but seeing the increased visibility of armed gangs with assault weapons at mosques and attacking Black Lives Matter protestors reminded me of nothing else than how politics in the Weimar era was literally fought in the streets.
For the first time in my life I am questioning whether America's democratic form of government will endure. The state now has a surveillance and carceral mechanism unparalleled in American history, just sitting around to be used by the powers that be against political dissenters. The police and military are routinely named the most trusted institutions in American life. The constant shutdowns and gridlock in DC make it easy to denounce regular politics, and for a "man of action" to get broad support. Donald Trump has jumped ahead in the Republican presidential race by attacking immigrants and Muslims, and promising to expunge them from the body politic. The leaders of the Republican party have been so weak that Trump insulted the military service of John McCain, one of their most venerable members, and were basically too chickenshit to call him out directly. They have a choice between standing up to the demagogue, pretending he will go away, or trying to co-opt him. They have tried choice #2, but #3 looks like it might be happening very soon in the future. I doubt he'd win, but it would be a sign now that all bets are off when it comes to whipping up the forces of nationalism and politicized racism.
Like the Third Republic, it might take decades of low-grade political civil war, but the result could very well be the same. In my darker moments, like today, I fear we may have crossed the Rubicon without even realizing it.