Good lord. National polls don't mean squat. Cruz could win 99% of the vote in the Southern States and he would still lose. It's questionable that even if the POTUS election was based on the popular vote that the polls are representative but they aren't.
Based on State polling Clinton starts off with a 40 EV lead on Trump. Trump would have to have nearly a clean sweep in the swing States to beat her. Assuming her campaign doesn't implode that's highly unlikely. Cruz, on the other hand, would be start out with nearly a 100 EV deficit.
Which means the odds makers are pretty much spot on with Clinton having a 3:1 advantage on Trump and nearly 8 to one on Cruz.
So the down side for the GOP is that Clinton is very likely to win and Trump or Cruz will bring down the Senate and house too. The GOP has a real good chance of losing the Senate.
The good news is that in four years, unless the GOP pulls another disconnected plutocrat or a Trump or a Cruz out of its ass, Clinton will probably be a one term President.