If a number of Obama states in the Midwest (OH, IA, PA etc.) flip to Trump, will the Democratic Party do anything to stop hemorrhaging working class white voters to the GOP?
No, because people like Joe Sestak and Jack Markell, with legitimate appeal to working class whites, keep being ganged up on or kept out of major league politics. Joe Sestak would be a good nominee if Bob Casey retires and Wolf runs for Senate or if Wolf doesn't run for Senate. If Joe Sestak, Jack Markell, or someone similar pulls out the nomination, they should easily beat Trump.
I think a moderate Democrat is going to have a hard time winning the primary in 2020 if Trump wins. Sanders supporters will be angry at Clinton and the Dem leadership for blowing the election. They would lower the tone down on identity politics and move to the left on economics.
What moderate Democrats are there? Evan Bayh, Henry Cuellar, Gwen Graham, Ralph Northam, and maybe Gavin Newsom are the only ones I could see maybe running for President.