I don't think he's weak on immigration, gun control or racial issues. I think you're overplaying gun control on the left as well. They're more than willing to put that behind them for other issues that Sanders is catering to. Sure he'll alienate a certain left looney or two with his gun stance. But it's pretty much right down the line with America. Address the issues for the shootings, not just the guns. Racial issues, he believes by addressing the financial issues we're having (income inequality if you would) many racial issues will dissolve. True he doesn't pander to race issues, but will that be a bad thing? It will make it harder to get elected, Hilary is likely to carry the black vote at an impressively high level, and Sanders will get hit hard in the South for that reason. For Immigration, Sanders has been on the record as being more progressive than Obama. But it's not one of his major talking point. His major talking point is jobs and economics. Shocker I know.