There are ways for US to retaliate through espionage, such as doing a mass round up of minor russian spy assets that usually aren't worth the effort to go after

There are ways for US to retaliate through espionage, such as doing a mass round up of minor russian spy assets that usually aren't worth the effort to go after, going after russian operations in places in which neither country have jurisdiction in, exposing blackmail of some random oligarch, stirring up unrest with plausible deniability, etc. Essentially make life difficult for the people who actually run Russia.