When President Obama announced an executive order on immigration in late 2014, he seemed frustrated by a Congress that was unwilling to pass what he called “common sense” reform.

Fourteen months later, immigration is one of the most-discussed issues of the 2016 presidential campaign, and Obama’s plan still hasn’t been enacted -- and may never be.

The plan would shield from deportation more than 4 million undocumented immigrants already in the United States. At the same time, though, the Obama administration is under fire over deportation raids that target mostly women and children from Central America. (Obama’s plan to give legal status to those 4 million immigrants includes only those who have been in the country for at least five years and are parents of U.S. citizens. It also would remove the 30-year age limit from a program that allows undocumented immigrants brought to the United States as children to stay in the country.)

A federal judge blocked the president’s executive order last February after 26 Republican-run states filed a lawsuit objecting to what then-House Speaker John A. Boehner (R-Ohio) called Obama’s “legacy of lawlessness.” Boehner said the president was “acting like a king,” rather than working with Congress to pass new laws.

The Supreme Court's decision on the matter is likely to be handed down early this summer, amid a presidential race in which immigration has become a central issue. GOP candidate Donald Trump wants to build a border wall, and rival Marco Rubio is under attack for flip-flopping on a path to citizenship for undocumented immigrants. Both leading Democrats in the race, Hillary Clinton and Bernie Sanders, have called for a path to citizenship, although that is unlikely to pass in a Republican-controlled Congress -- the same hurdle Obama tried to overcome with his executive order.

But even if the Supreme Court upholds Obama’s order, it isn’t guaranteed to be around for long; his administration has only a year left, and the next president will ultimately decide whether to keep the program.