Donald Trump officially, if belatedly, rolled out Mike Pence as his vice presidential choice Saturday. While many Republicans who have otherwise been skeptical of Trump were happy, some of the New York businessman’s biggest fans are not.

The biggest reason is immigration. Ten years ago, while still a member of Congress, Pence floated what he described as a “middle ground on immigration.” He argued in an op-ed for the Wall Street Journal, “[M]y bill does not include a so-called path to citizenship, i.e., an amnesty, for the some 12 million illegal aliens in this country.”