(1) Majority-minority breakdowns assume anyone with "mixed-blood" is not "white." If everyone with one white parent is considered white, we'd count the US as 75% "white" in 2050 instead of <50% "white". Furthermore the label "white" might become more inclusive.
(2) The young are more liberal than older people. But research shows that people get more conservative over lifetimes. Todays young people aren't out of the historic norm for liberal. And America is getting older not younger