This chart reflects the results of the latest Economist / YouGov Poll -- done between July 21st and 23rd of a national sample of 1,212 registered voters, with a 2.9 point margin of error.
The poll's respondents were asked which party best represents each of several groups. It looks to me like the Democratic Party fared better, and is probably the reason they are favored in electoral polls.
The Republicans were seen as caring more for corporations, rich people, Whites, and men.
The Democrats were seen as caring more for "people like me", workers, families, legal immigrants, undocumented immigrants, the middle class, poor people, Blacks, Hispanics, and women.