I once heard a full of himself conservative talk show host, who will remain nameless, scoff at the notion that the Republican Establishment was capable of "picking Mitt Romney." His point was that it's up to the voters, the Establishment can tell them who to vote for. That position is downright child-like in its naivete. The Establishment sure the hell can dictate your choice by limiting who you can vote for in a presidential primary.
Everybody wondered why the "A" list of candidates, Rubio, Ryan, Jindal, Christie, stayed out of 2012. Yes, family concerns and other reasons cited were real. But they also knew the Establishment had placed its bets with Romney shortly after the November 2008 election. You could see the same thing in 2016. It's widely believed that Rubio, who sees Jeb Bush as a mentor, will not run if Bush does. And it's likely that Paul Ryan, Bobby Jindal, Chris Christie and any other perceived A-lister, including Scott Walker, won't challenge the chosen Establishment candidate.
It's one of the reason the U.S. Senate primary in Wisconsin was as ugly as it was. The party establishment was firmly behind Tommy Thompson, even if they tried to do it covertly. It was considered poor form for other legitimate contenders to challenge him. The above mentioned A-listers will stay out if they're convinced the party machinery has settled on Jeb Bush. And as long as Tea Party favored candidates follow Establishment Republican etiquette, this is how the Establishment can virtually choose the nominee.