Even if you grant that raising the minimum wage is a good thing (which it isn't), it's a proposal that only effects a few million people out over 120 million voters -- and most of those few million are poor people who are most likely democrats.
How does a proposal aimed at such a small minority of the population make it as a major campaign plank?
Are you figuring in all the union people who have their wages set relative to the minimum wage?
It also makes their touchy-feely liberal base feel good as they motor around in their $50,000 a pop SUVs. Think of it as a sort of a personal excuse from having to practice any sort of charity. "Wow, higher minimum wage! Government IS taking care of it!"
"raising the minimum wage ...How does a proposal aimed at such a small minority of the population make it as a major campaign plank?"
Because (1) a lot of Union contracts are tied to minimum wage as a multiplier factor i.e. the lowest paid guy gets 5 times minimum wage etc...
(2) Your forgetting the "feel good" factor of people who make way more than minimum, but "feel good" that the "little people" are getting a few crumbs more on someone elses dime.