In 2012 an unpopular president--presiding over a 'bad economy', supported by an unenthusiastic base, and having been out-debated by a credentialed challenger--won reelection by a comfortable margin. Time is obviously on the Democratic party's side, so as propitious as the circumstances were for the GOP in 2012, they'll have to be even more favorable in the future for Republicans to have a shot at winning a national election.
Texas births in 2014, by race:
When the inevitable consequences of this demographic transition flip Texas from red to blue (in 2032 if I had to guess), the game will officially be over. For those familiar with the American political landscape, that might seem difficult to fathom at first blush. Consider, though, that from 1952 through 1988, California was a solidly Republican state, voting Democratic only once during that 36 year period. Now, of course, California is one of the most reliably blue states in the country.
Parenthetically, this is not to bemoan the decline of the Republican party per se. To the contrary, I've come to view its diminution as a good thing (and not only because it means fewer military blunders into third-world hellholes). The sooner a critical mass of people realizes that the idea of the US as a unified political entity is unworkable, the sooner secession becomes conceivable. Effective one-party rule is a great way to expedite that process.