Ten years ago, mainstream pro-Israel groups carefully avoided the issue of West Bank settlements; today, politicians who argue that settlement expansion is an obstacle to peace — a longstanding American position — risk being tarred with the anti-Israel brush. Even though support for settlements reflects the perspective of a small minority of American Jews, it increasingly appears to be the policy stance of major pro-Israel groups.

It was precisely this sort of fringe-driven politics that accounted for the Republican Party’s dramatic electoral losses. Wild conspiracy theories about President Obama, extreme positions on popular entitlement programs and offensive remarks by candidates who spoke of things like “legitimate rape” turned voters off in droves. More moderate party leaders, fearing the wrath of the radicals in their ranks, were timid in repudiating those positions and comments, and fed the impression that they were in agreement.

Judging from the National Rifle Association’s clumsy news conference last week, the gun-rights lobby may be nearing a similar public relations cliff. By playing to zealots who reject any government restrictions on firearms, they are not lobbying for the right of hunters to keep their deer rifles, or homeowners to keep their revolvers; they are arguing for the right of anybody, including the most demented people, to own the most lethal firearms, and making the absurd claim that the more Americans who are armed, the safer we will be. As a result, the N.R.A. may soon see its support evaporate among those in the persuadable (and reasonable) middle.

Playing to the extremist fringe could produce short-term gains for pro-Israel groups by rallying the faithful and encouraging big contributions. But — as this year’s election and rising anti-gun sentiment demonstrates — it brings with it the risk of a popular backlash.

Support for the Jewish state remains strong among both parties on Capitol Hill and across the American electorate, and it won’t disappear anytime soon. But that support will wither if Aipac and other mainstream Jewish leaders don’t forcefully reject the zealots in their midst.

And, in the long run, that can only damage the interests of a vulnerable Israel.