The Obama administration will probably file a lawsuit against Arizona over their new immigration law; per Jake Tapper it might come next week. Some GOP leaders are encouraging that party to use it as a campaign issue, but according to this (obviously speculative) report, John Cornyn - chairman of the National Republican Senatorial Committee - might be the sticking point:

But the consultant, who has urged clients to take a strong stance on immigration, does not expect Cornyn to make the Arizona law a national issue to batter Democrats, for fear of offending Hispanic constituents at home.

“Sen. Cornyn is stuck between a rock and a hard place. He’s being very good about balancing it, but at some point he’ll be called to task and asked, ‘Where are you?’ ” said the consultant, who requested anonymity because Cornyn could influence the hiring decisions of potential clients.

Recall that Cornyn was involved in helping Sonia Sotomayor get onto the Supreme Court by putting up a sham opposition. See his name's link above for more, and do a search for many more past entries.

You can contact him through cornyn.senate.gov