The Republicans are very good at gerrymandering and using voter suppression in swing states.
As to the second point - there is some merit to the point that the remain campaign was complacent but then that means you accept that the Remain argument was better but the campaign worse as how else were they complacent if they didn't have the better argument. Which is now being played out right in front of us. In the end we need to do what's best for the country which is not Brexit.