Become more moderate and pro white and more blue collar and nominate someone more like Jim Webb and less like Hillary Clinton and Bernie Sanders
That won't work. While I think Democrats should definitely drop the gun issue, (and the abortion issue as a litmus test) pandering to whites and blue collars will just make them another brand of Republican lite. People will vote for the real thing (Trump) in that case. It's time to go hard left on economics, appealing to millenials, poor minorities and the working class. Stop identity politics altogether (pandering to any segment, be it minorities of whites) and focus on issues that will bring everyone together.