Bernie, Warren, Harris, etc. speak directly to issues which disproportionally affect other groups (police violence against blacks, immigration policy that mainly affects Hispanics, etc.), but never this one. It gives an impression of unequal treatment, and leaves some feeling unnoticed and ignored. This creates opportunity for the first politician to say, "I see you, I see your suffering, and I will not ignore you."
I don't know if she says "rural whites" verbatim, but Warren talks about rural issues all the time. It's one of the central tenets of her campaign -- that previous Democratic candidates (other than Sanders) ignored rural America, and she isn't. She campaigns in small rural towns that few other candidates will campaign in.
https://medium.com/@teamwarren/my-plan-to-invest-in-rural-am...