Did Obama lose the youngest voters? I thought he won them 60-37. He did however lose white youth to Romney, but only 49-48.
Any GOP candidate that wants to turn back the clock on same-sex marriage (think Ted Cruz) is doomed among young voters. The GOP will have to face reality on this issue, just as they did once upon a time with social security, among other issues.
As a whole, yes, Obama won Millennials overwhelmingly. However, in 2012, due to the factors I listed, he did lose the very youngest voters, 18 - 20 year olds. 18yr olds: 57% Romney, 19yr: 59%, 20yr: 54%.
I don't think the sample size was very big there.
Anyway, the parties will have to evolve as the population evolves.