New York Magazine's Jonathan Chait sees the GOP's push for immigration reform as a battle between the GOP elites and the GOP base:

And so, among other things, the party’s ability to make this decision stick will be a test of its ability to wrest control from the activists. One constant and somewhat unusual dynamic of the last few years is the degree to which Republican base activists — grassroots ones, not the ones based in Washington — were able to bend the party to their will. They repeatedly nominated ultraconservatives in Senate races over Establishment favorites. They dragged out the presidential campaign and forced Romney to endorse draconian positions, especially on immigration, that hurt him dearly.

The concerted campaign, spearheaded by Marco Rubio, to make immigration reform acceptable is the biggest test case of whether the party leadership, such as it is, can bend the activists to their will. It won’t be the last.