Although not "modern US" in most considerations, I believe that West from Appomattox by Heather Cox Richardson is essential for understanding the Republican Party, Reconstruction, and the politics of the West.

For Depression Era/New Deal, I think Ira Katznelson's Fear Itself is fantastic.

I also enjoyed Barbara Key's Reclaiming American Virtue for a post-Vietnam look at wrestling with what American would, nominally, stand for.

The Rise and Fall of Modern Conservatism by David Farber tracks, well, just what it says it does.