1. McCain lost because things weren't going too well either at home or abroad. Romney lost because he was the guy who hired the guy who fired you. Lots of stuff has changed since 2012 (Obamacare flat-tired "roll-out"; Isis, anybody?) and so I don't think these things are really all that relevant now.
2. The social justice warriors control the Democratic Party, partly because the public sector unions provide the cadres and a big chunk of the money, partly because Soros, who has made his money shorting freedom, back them to the hilt.
3. A lot of Latino citizens are coming around to the Sonny Bono/Yakov Smirnoff position on illegal immigration -- the collapse of public order in Mexico is helping to drive this. A Republican who goes for amnesty loses his base, and cannot gain much in general against the social justice warriors.
4. In the next two years we will see a Christian Minister going to jail for refusing to perform a homosexual "marriage." That is going to push a lot of Black church ladies away from the Democratic party.
5. Two more years of nastiness between Congress and the President is bad for the country and the world. Democratic control of Congress from 2006-2010 got us where we are today on the economy and Iraq. A Presidential system isn't all roses...