Well it's pretty much the most important question that the GOP has if they want to take the presidency.
Here is the Red/Blue electoral vote map from 2012. 
The Electoral College Vote was:
Obama: 332
Romney: 206
270 needed to win.
Flipping Colorado would be a good start, and add 9 to Sen. Cruz's total, taking him to 215, but he still would need another 55 EV's to get to 270.
Flipping Florida (29), Ohio (18) and one of Michigan (16), Pennsylvania (20) or Wisconsin (10) would do it.
So would just Florida and New York (29).
Now, perhaps, you are seeing Ted Cruz's problem. He's most attractive in Red States, and not so attractive in Blue States.
It's (at least to me) a lot harder to imagine him finding 64 total electoral votes than it is imagining Trump doing so.