Most of the interstate highway system, any number of lakes, many major bridges, the completed portion of the superconducting supercollider underground chambers, the brilliant Alaska pipeline pylon system, Florida's long elevated marine highways, the Norfolk (?) tunnel, the NYC aqueduct, most major airport runways.
What man has done he may aspire to do again.
These things move in cycles. Political patronage projects currently are in vogue, but their star is falling. You cannot credibly claim that unions will make any LA-SF project cost $100B, because Mr. Bond Market is about to have a mountain comes to Mohammed moment. At some point the market for rational projects will reopen for a few decades, like it does from time to time.
Elon Musk is just the man to make it happen. He already killed the Space Shuttle program and its standing army of $1B/yr payroll patronage jobs. Extending that to other projects is a matter of will and personality.