Put another way, if you are just against someone vs being for someone then your field of candidates is incredibly weak.
Simply being AGAINST someone doesn't win elections. Rubio is a bad candidate for POTUS bc outside of his one liners he has very little substance or record to back himself up as a viable candidate. Ted is a bad candidate bc he frightens everyone with his Jesus talk (yes it is frightening). John K is probably a good candidate but it is the wrong point in history for someone like him.
Trump has tapped into the American soul of discontent (so has Bernie in a similar but slightly different way) now add in his ability to manipulate the media and mix it with his marketing/branding skills and you have a guy that is riding that wave to the nomination.
I don't blame Trump as he is just a symptom of the environment that the establishment of the R and D parties created the past 20 years. Everyone realizes that party politics is ruining our country, now American's are voting against the system...you may not like the candidate but good for them in doing so.
I pretty much agree with all of this, although I may like Rubio more than you do. I think Kasich, Christie and Bush also could have been solid, viable candidates under different sets of circumstances, but clearly those actually participating in the GOP process right now aren't looking for that kind of candidate. I've pined for a good, solid outsider for a long time. I actually voted Perot in 1992, but I just wish it was someone other than Trump, who I find to be entertaining in a reality show sense, but a probably disaster as POTUS.
No matter how all of this turns out, it's pretty clear that the GOP is going to go back to the drawing board or else an upstart party would have to see a window here to pop up and make some noise.