Large parts of the US are ideal for high-speed rail.

The Eastern Seaboard is basically perfectly laid out for high-speed rail (Boston - NYC - Philadelphia - Baltimore - DC). The Midwest has tons of ideal city pairs, such as Chicago - Detroit or Chicago - St. Louis. Even a line between Chicago and NYC would be practical (3.5 hours downtown to downtown with modern HSR).

The main problems for HSR in the US are: extremely car-centric development, highly individualistic politics, incapability of pulling off large public projects.

That is true in a broad sense, but there are certainly many city pairs / areas where cities are within few hundred miles of each other. For example, there are flights from SF to San Jose, there are flights from Chicago to Madison, there are flights from Chicago to St Louis and so on. All city pairs where a HSR would be faster / same time duration as a plane end to end.