This front page post by Sher Watts Spooner on proposed Democratic messaging for the 2018 midterms shows the power of white male identity politics, in large part because it's still white males that run a party whose rank and filers are increasingly not white or male.
Aging white male Democratic leaders like Joe Biden and (as shown here) Chuck Schumer may not agree with aging white male Democratic Socialist Bernie Sanders and his core followers on many things, but they are as one on this issue: the perceived need to re-center white males in the Democratic Party even as America's getting less white with each passing day.
The winning message for Democrats in 2006 was: Stop Bush.
The winning message for Democrats in 2018 is: Stop Trump.
George W. Bush and the rest of the GOP spent 2005 trying to destroy Social Security. This angered even many Republican voters, and led directly to the Democratic wins of 2006.
Donald J. Trump and the rest of the GOP are spending 2017 trying to destroy Medicare and Medicaid as well as the ACA. This is angering even many Republican voters, and will lead directly to big Democratic victories in 2018... but only if Schumer and Biden get over their desire to re-center white male wishes as the party's raison d'etre.
Want a simple message? There's your simple message.