Apparently 51 percent of the American people support Arizona's new immigration law. At first blush, this would suggest that politicians would be smart to align themselves with it, as Colorado Republican gubernatorial candidate Scott McInnis has done. On the other hand, as Kos notes, Prop. 187 passed with huge margins in California back in 1994, and no Republican has won a gubernatorial, senatorial, or presidential race in that state since (with the exception of a very moderate Schwarzenegger in a very fluky recall election). So what's the deal? Is the Arizona law toxic? To whom?
One of the key things to remember about midterm elections is that turnout is low compared to presidential elections. It tends to be the angrier voters who show up -- people who have some sort of policy axe to grind -- which is partly why the president's party tends to lose seats in these elections. People who are happy with Obama's agenda have far less incentive to vote in November than those who want to stop it.
So the 51 percent who are okay with the Arizona law are not necessarily reflective of those who will turn out to vote in November. The vast majority of Americans can probably conjure up an opinion on the law but won't be motivated to vote because of it and won't base their vote choices on candidates' stances on the law. Latino voters, however, suddenly have a dog in the fight. I would say the percentage of Latinos likely to vote in November just shot up significantly, and if any of them were considering voting Republican post-Sotomayor, they're probably not now. So I tend to think that the Arizona law activates a sizable chunk of Democratic voters for November without necessarily activating many Republicans. In that sense, aligning oneself with the law, as McInnis has done, might be risky.
That said, I'm not sure that there's a direct causal relationship between California's passage of Prop. 187 and Democratic successes there in recent years. The state had been trending Democratic for many years, and Dems had controlled the statehouse pretty consistently since the late 50s. The GOP got a boost there thanks to Reagan's presidential runs, but the recent successes of the Dems are probably more due to a general trend of polarized parties -- voters are less likely to vote for a candidate of a different party, and parties are nominating more extreme candidates. Pete Wilson, California's last Republican senator and governor prior to Schwarzenegger, was pro-choice, for heaven's sake.