The NERVA project was the closest we got. NASA was ready to build a prototype and send it up for testing and it actually had support in Congress (unlike every other non-Shuttle thing), but Nixon killed it out of spite because Congress killed the American Concorde project. Some people in Congress even tried to tie it to the Shuttle (imagine the possibilities of Shuttle launch nuclear thermal kick stage) but Nixon being the petty b*tch he was told NASA to not use the money Congress allocated for it.