I'm not sure I agree with David Brooks' implication that anti-immigrant appeals will be bad short-term politics for the GOP, but his larger point here seems quite correct:
At the moment, Giuliani and fellow moderate Mitt Romney are attacking each other for being insufficiently Tancredo-esque. They are not renouncing the policies they championed as city and state officials, but the emphasis as they run for federal office is all in the other direction. In effect, they are competing to drive away Hispanic votes and make the party unelectable in New Mexico, Arizona, Colorado, Nevada, Florida and the nation at large.
In this way, they are participating in the greatest blown opportunity in recent political history. At its current nadir, the G.O.P. had been blessed with five heterodox presidential candidates who had the potential to modernize the party on a variety of fronts. They could be competing to do that, but instead they are competing to appeal to the narrowest slice of the old guard and flatter the most rigid orthodoxies of the Beltway interest groups.
It's genuinely strange. You could imagine a Republican primary being dominated by orthodoxies because all the candidates had fairly orthodox records, or because a party riding a favorable political wind saw little need to rethink anything. The Democratic field seems to be experiencing a combination of the two. But the Republicans are in the reverse situation. Their party's generic brand is in terrible shape, they're losing in the early polls and in the fundraising battle, and they have tons of candidates at hand with semi-heterodox records. But they're all compete to adhere ever-more-rigidly to the hard-right line on immigration and on taxes and on the war.