Mitt Romney’s father, George Romney, has been invoked on the campaign trail often. Newt Gingrich used his release of 12 years’ of tax records as an example to push his rival to release his own tax returns. On Thursday night, Romney mentioned the fact that his father was born in Mexico in response to Gingrich’s allegations that he is “anti-immigrant,” which raises the question: If George Romney was born in Mexico, how could he run for president?