Most of the current crop of Republican nominees at one time or another during this cycle have said something to the effect of "any one of the people on this stage would be much better qualified to be president than Hillary Clinton". They may not have not said those exact words, but even Donald Trump finally ruled out a third party run at the last Republican debate. They all want to win, and most of them are team players - not Jeb Bush.
Bush spoke in an interview with CBS’s Face the Nation scheduled for broadcast on Sunday and taped in New Hampshire on the same day he told a town hall audience Trump was a “jerk”...On Friday, through Twitter, Trump called Bush “dumb as a rock”. He returned to the offensive on Sunday morning.“To a certain extent, it is a little liberating to be able to post up against a guy who is not qualified to be president,” Bush said in the CBS interview, which was excerpted by the website Politico.“I’m trying to point out that he’s not a serious candidate.
And there you have it - if I can't win I'm going to torpedo the guy who looks like he might win the GOP nomination because I'd rather help the Democrats the the Republicans, if Republicans don't pick me. He can't pretend that those words won't hurt Trump if he winds up winning the nomination.
And while Trump is not the ideal candidate, he's doing well for a reason. Bush doesn't seem to get that, and it's alienating voters at a rate so quickly that his Super PAC money won't help him recover them. More importantly from a winning the White House perspective, if Bush is saying this about Trump, why wouldn't he say it about Cruz, Carson, Fiorina, Paul or even Rubio or Christie if they end up taking the lead?
Addendum: Yes, I realize that calling Jeb Bush a jerk is sort of doing the same thing as Bush is doing to Trump. Don't care. I'm offending 3%-5% of Republican voters (less because my readership at best probably numbers in the hundreds most of the time), while Jeb Bush is offending 20%-40% of GOP voters depending on which poll you believe, and in fact more if every Hillary Clinton ad turns out to be quotes of Jeb Bush slagging the nominee Trump. Besides everyone on the right should feel free to slag Bush. No one in that family is a true conservative, and there is no chance he'll end up the nominee.