So what happened? It depends on whom you ask. But the inescapable lesson is: Trump’s administration has become so radioactive that the president can’t bring in one of his party’s most promising stars, one of his closest allies in the Republican establishment, to take such a prominent post.But Vox also says Trump might not have wanted to open up Cotton's Senate seat. Also, maybe Cotton — mean but no dummy — decided Trump might lose in 2020. Or maybe the ambitious Cotton decided he could build his own national ambitions better in the Senate.