Demonstrators march against amnesty for illegal aliens, during a rally against the immigration reform bill in Pennsylvania Avenue in Washington July 15, 2013. The U.S. Senate passed sweeping immigration legislation at the end of June. But the legislation's fate is unclear in the Republican-controlled House, where Republicans are adamant against approving the Senate version of legislation and are instead talking about passing several bills that address various immigration problems, but not necessarily legalizing the estimated 11 million undocumented residents. REUTERS/Jose Luis Magana (UNITED STATES - Tags: POLITICS SOCIETY IMMIGRATION CIVIL UNREST) Demonstrators march against amnesty for undocumented workers on July 15 in Washington. (Reuters / Jose Luis Magana)

Thursday marks the one-year anniversary of the start of President Obama’s deferred deportation program for immigrants brought to the country illegally as children, which he authorized through executive authority last summer. As The Washington Post reported Tuesday, the Obama administration has granted more than 400,000 of those immigrants temporary legal status to work or go to school without fear of deportation.

Now, Sen. Marco Rubio (R-Fla.) is warning that the administration is likely to dramatically expand the program to cover the majority of the country’s 11 million undocumented immigrants if Congress fails to pass comprehensive immigration reform.