Don Young is helping.

Heading into the immigration debate, Republicans were probably hoping not to cast themselves as agricultural barons perched on a rocking chair, surveying Latino immigrants as so much disposable labor. Yet here was Republican congressman* Don Young yesterday, reminiscing, “My father had a ranch; we used to have 50-60 wetbacks to pick tomatoes.” Also, dude: “Wetback” is not the preferred nomenclature.

Maybe one way to think about Young’s gaffe is as evidence of the cultural barrier that makes it so wrenching for Republicans to embrace comprehensive immigration reform. But the better way to think about it is that comments like Young’s are why immigration reform will probably pass.

The 2012 election crystallized the Republican Party’s fears of a growing Latino electorate increasingly convinced of the GOP’s hostility. But the foundational event for this fear is the immigration-reform debate that took place during George W. Bush’s second term. A grassroots conservative revolt forced Bush to abandon reform, but worse than the outcome was the process — old, white, right-wing vigilantes on the border snarling about immigrants, and old, white, right-wing Republicans in Washington doing the same, all transmitted over the Spanish-language media.

The process repeated itself during the GOP primary debate, when candidates jostled to stake out the harshest available stance, and Mitt Romney prevailed by painting no less a figure than Rick Perry as Uncle Sucker, handing out free gifts to “illegals.” Not surprisingly, the Republican commission charged with patching up the party’s image proposed limiting debates and controlling their sponsors to avoid putting the spectacle of candidates openly catering to the prejudices of the base on public display.

The immigration debate, more than the immigration bill, is what Republican leaders fear — the prospect that even a few poorly crafted comments will come to define the party’s true beliefs. Carlos Guitierez, George W. Bush’s Commerce secretary, expressed the fear in January. “Of course I’m worried about it. A few people give the party a reputation,” he said. “If they’re not going to support [immigration reform] I hope they at least can keep quiet about it and manage their language and body language.” Even critics of reform hung their hopes on strict partywide verbal discipline. “If the tone of the debate is thoughtful,” then Republicans can survive politically even if they reject “blanket amnesty,” said GOP strategist Terry Nelson last month.

The fear of such a poisonous debate is the key strategic fact. Republicans would probably prefer to avoid any immigration-reform debate, and thus close off the risk that the Don Youngs of the party run their mouths. But the presidency offers Barack Obama the power to hold an immigration debate, and so Republicans can only choose between bad options.

An ugly debate and a rejected bill mean repeating and compounding the debacles of the recent past. But passing a bill gives Republicans a happy ending. There will be gaffes, but the final picture will be Republican leaders standing beside Obama in the Rose Garden, and the reform itself, rather than the debate, will be the lingering impression.

The uglier the debate, the more imperative it becomes that Republicans find a way to change the ending and prove that the Don Youngs don’t really speak for them.

*This posted has been corrected to show that Young is a congressman, not senator.