In terms of the impact it could have in November, the most important moment of last night’s debate may have come when Mitt Romney hailed the Arizona immigration law as a “model” for the nation while Sheriff Joe Arpaio beamed approvingly:

After moderator John King noted that Sheriff Arpaio said it was “political garbage” to not arrest and deport illegal immigrants, and asked Romney if he supported “aggressive” arresting and deportation, Romney went further than just endorsing Arizona’s approach.

“I think you see a model in Arizona,” Romney said, citing the employment verification system, stepped up border patrols and a border fence as goals for his presidency. “You do that, and just as Arizona is finding out, you can stop illegal immigration,” Romney said, adding that he would halt lawsuits against the Arizona law “on day one.” Santorum went even further.

I don’t know how this plays among swing voters — some polls have shown national support for the Arizona law — but if Obama and Dems can make this stick, Romney may have ended any hopes of making any real inroads among Latino voters. And that could have far reaching ramifications in the general election.

One key route to reelection for Obama runs through the western states — what Obama advisers call “the west path.” He can offset expected losses in the Rust Belt but still win reelection by holding on to Colorado, Nevada and New Mexico. Demographic shifts in the west — rising minorities and falling numbers of working class whites — are more favorable to Obama than in the Rust Belt and midwest region. Latinos could be pivotal here.

More broadly, yesterday’s moment crystallizes a broader set of rising concerns among Republican operatives. They worry that the GOP primary is forcing the candidates to take a tone that’s compromising efforts to rebrand the party as forward looking and inclusive. Even before yesterday’s debate, Louisiana Governor Bobby Jindal warned against coming across as the “anti-immigrant” party, arguing: “We need to be more articulate in voicing the aspirational spirit of America.” And so moment’s like yesterday’s could help damage the GOP in ways that impact November.

Obama’s own record on immigration has been disappointing in some ways. But as Adam Serwer notes today, by clearly signaling what they would do on immigration as president, the GOP candidates may have saved Obama from his own record and given Latinos a reason to come out for Obama in the numbers he needs.

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UPDATE: Steve Benen has a rundown on the other ways Romney has lurched to the right on the issue, concluding: “Romney, by any reasonable measure, is the most right-wing candidate on immigration of any competitive presidential hopeful in generations.”