Former Mexican President Vicente Fox claims that most "illegal immigrants" from Mexico have no interest in becoming US citizens:

Fox said most illegal immigrants from Mexico don't want to become U.S. citizens and plan to return to their homeland someday because "they like better tacos, tortillas and chilies than hot dogs or hamburgers." He thinks a temporary guest worker program would solve many problems.

John McCain's "Hispanic Outreach Director" Juan Hernandez (a former adviser to Fox) has also said that immigrants to the US from Mexico should not/will not "assimilate."