You might want to take a look at this analysis from Pew Research of political party affiliation by gender, race, age, and educational attainment. Superficially, it looks pretty bad for the Republicans and it would be if party affiliation were as rigid for the Millennials as it is for, say, African Americans.
It used to be believed that once young people had settled on a political party they rarely budged but that seems to be an oversimplification. What is now believed is that certain life milestones, e.g. getting a job (or failing to), having children, buying a first home, etc., motivates people to re-evaluate the views they’ve held.
It still looks pretty obvious that Republicans can’t be successful at the national level and be the old white guys’ party.
Well, I’m a libertarian, and while voting for a Republican, even Rand Paul, makes me hold my nose, I couldn’t see ever voting for a big-gummint Democrat. Gummint is the enemy, in almost every case.
“Republicans have leads among whites – particularly white men, those with less education and evangelical Protestants – as well as members of the Silent Generation.”
Charlie Cook gave a more succinct characterization: The GOP — certainly its base — is the party of the pre-dead.
The GOP is the party of married white people with children. Everything that makes child rearing in the confines of marriage less attractive is a win for the Democratic Party.