"The Hispanic population has taken on a momentum of its own," said Kenneth Johnson, senior demographer at the University of New Hampshire's Carsey Institute. "If you close the borders tomorrow, there is still going to be a large Hispanic increase." That's from a Wall Street Journal writeup of a Census report on the fast-growing Hispanic population, showing that a bit over 60 percent of the increase is attributable to the Hispanic birthrate rather than to immigration.
This is why I think the GOP has probably dodged an important medium-term bullet by nominating John McCain. For a while it looked like there was a very real chance that the Republicans were going to abandon the immigrant-friendly posture that's helped their party do well with more prosperous Latinos in favor of embracing a politics of Anglo ethnic panic that could have been enormously harmful over time. At the non-presidential level, though, the right still seems quite invested in crackdown policies and McCain has made some significant gestures in that direction during the primaries so it remains to be seen what they'll start busting out if things look bad in the fall.