The only way I see the Democrats losing the White House is a Sanders/Rubio general with Rubio finding a way to draw huge numbers of Hispanics to his side. Even then, I think it's probably close. Sanders probably beats Cruz. Sanders definitely beats Trump. Clinton beats everybody. Maybe Rubio has an outside shot if the stars align. The problem with Republicans is that they've corralled 4-5 truly terrible candidates and one mediocre candidate who might be young enough and vibrant enough to draw some traditional Democratic voting blocs across the aisle. Then again, Rubio's policies might keep independents, young people, and people of color away from him so he loses just like the rest. But he probably brings the GOP Florida, which is huge. I know you like Cruz but when/if he hits the national stage and the mud really starts flying, he's going to be crucified because everyone will realize he's eminently unlikeable. Not just a little unlikeable, which can be overcome... But really unlikeable. The guy has the charisma of a basilisk. On top of all that, the GOP has crafted a platform that makes it nigh impossible for them to win most of the large electoral states. Their platform works for state-level and local level elections but it adversely affects them when it comes to a nationwide general. Automatically writing off 130+ electoral votes is a difficult hurdle to overcome. They can't win the west coast, they can't win the NE with the possible exception of PA, they can't win MI, IL, MN, etc. Meanwhile, Democrats have one populated state they cannot win: Texas. The rest of the Dems' unwinnable states are mostly in the 3-9 electoral vote range. The Republicans have to make nearly a clean sweep of the plains states, south, and southwest to even make it close.