I don’t think Jeb Bush’s position on immigration is fatal to his chances of winning the 2016 Republican nomination for all the reasons Ramesh Ponnuru describes and several others besides. Bush’s support for a combination of policies that include legalization before effective enforcement and increasing future low-skill immigration probably is not the most popular position among Republican primary voters, but that doesn’t have to be a deal breaker.
As Henry Olsen pointed out, the key group for winning the Republican presidential nomination are the “somewhat conservative” voters. I suspect that if you asked these voters if they wanted legalization before enforcement and increased low-skill immigration, a majority would say no. But that isn’t the end of the story. Don’t underestimate how much ideological deviation Republican primary voters will tolerate as long as a candidate seems administratively competent, mentally stable, well informed, right on most of the issues, and a plausible general election winner. Republican primary voters are especially forgiving if it seems that the more consistently conservative alternative seems to lack administrative competence or seems like a general election loser. The somewhat conservative voters seem willing to trade some policy disagreement in return for the assurance that a candidate has a decent chance to win an election and govern effectively. With the possible exception of having a plausible chance to win a general election, Bush passes all the test easily.
One other advantage of Bush is that manyof his likely Republican opponents are pretty similar to him on immigration. Scott Walker sure sounds like he wants to increase low-skill immigration. So does Bobby Jindal. To the extent that he seems to understand the issue, Mike Huckabee sounds a lot closer to Jeb Bush than his fellow Arkansan Tom Cotton.
Whatever opposition exists within the Republican nominating electorate to the kinds of positions favored by Jeb Bush will only be effective if it is embodied in a candidate who is a plausible president. Like Henry Olsen says, the key voting block in the Republican primaries is voting for a president, not a position paper or an attitude. If the opponents of Jeb Bush-style immigration policy are known for making offensive and incendiary remarks (or otherwise seem unserious ), then even some conservatives who disagree with Bush on immigration will swallow hard and vote for Bushor someone who has more or less the same immigration views as Bush.