All across the nation, there are mainstream Republicans lamenting how the party has grown more and more insular, more and more rigid. This year, they have an excellent chance to defeat President Obama, yet the wingers have trashed the party’s reputation by swinging from one embarrassing and unelectable option to the next: Bachmann, Trump, Cain, Perry, Gingrich, Santorum.

But where have these party leaders been over the past five years, when all the forces that distort the G.O.P. were metastasizing? Where were they during the rise of Sarah Palin and Glenn Beck? Where were they when Arizona passed its beyond-the-fringe immigration law? Where were they in the summer of 2011 when the House Republicans rejected even the possibility of budget compromise? They were lying low, hoping the unpleasantness would pass.

The wingers call their Republican opponents RINOs, or Republican In Name Only. But that’s an insult to the rhino, which is a tough, noble beast. If RINOs were like rhinos, they’d stand up to those who seek to destroy them. Actually, what the country needs is some real Rhino Republicans. But the professional Republicans never do that. They’re not rhinos. They’re Opossum Republicans. They tremble for a few seconds then slip into an involuntary coma every time they’re challenged aggressively from the right.

Without real opposition, the wingers go from strength to strength. Under their influence, we’ve had a primary campaign that isn’t really an argument about issues. It’s a series of heresy trials in which each of the candidates accuse the others of tribal impurity. Two kinds of candidates emerge from this process: first, those who are forceful but outside the mainstream; second, those who started out mainstream but look weak and unprincipled because they have spent so much time genuflecting before those who despise them.

Neither is likely to win in the fall. Before the G.O.P. meshugana campaign, independents were leaning toward the G.O.P. But, in the latest Politico/George Washington University Battleground Poll, Obama leads Mitt Romney among independents by 49 percent to 27 percent.

Leaders of a party are supposed to educate the party, to police against its worst indulgences, to guard against insular information loops. They’re supposed to define a creed and establish boundaries. Republican leaders haven’t done that. Now the old pious cliché applies:

First they went after the Rockefeller Republicans, but I was not a Rockefeller Republican. Then they went after the compassionate conservatives, but I was not a compassionate conservative. Then they went after the mainstream conservatives, and there was no one left to speak for me.