Immigration proponents worried about the future of reform in Congress have made clear their backup plan is to ask President Obama to use his executive authority to defer deportations for 11 million undocumented immigrants.

But one leading Republican advocate for reform said that would be a "big mistake."

Former Homeland Security Secretary Michael Chertoff believes a unilateral move by the White House would further doom the chances of Congress embracing sweeping reform legislation. Chertoff, who advocated for sweeping changes to immigration law under President George W. Bush, said Obama's election-year decision in 2012 to defer deportations for immigrants brought to the country illegally as children has caused great skepticism among reform opponents.