Well, that IS the Democratic Party playbook. As long as he looks and sounds viable, I don’t see how Hillary would have any better shot against him than she did against Obama.
I don’t think Carson will run. Allen West is possible but his primary opponents will try to make him look weak for losing his House race, despite the fact his own party tried to district him out.
The immigration debate is killing Rubio at the moment which is a shame because he would have been at the top of the GOP list. Perhaps Ted Cruz? As Nikki Healey recovered from the Romney endorsement? Bobby Jindal?