He can't. He's a reactionary capitalist, for starters, so he doesn't know how (note the rejection of "single payer", or the idea that he can repeal and replace Obamacare simultaneously and very soon) and doesn't actually see any need (nobody's banging on the door at the moment). And he's President, not Congress, so he doesn't have the power. Paul Ryan's Speaker of the House. When he gets on board with Government Care, it has a chance - not before.