U.S. immigration reforms could be passed now but enacted after President Barack Obama leaves office if Republicans fear he will not enforce the new rules, a key Democratic senator said Sunday, offering a way to achieve one of Obama's main policy objectives.

Last week, Republican House Speaker John Boehner expressed doubts Obama's long-sought overhaul of immigration laws would be passed this year and Senate Minority Leader Mitch McConnell said there was little interest in the issue with congressional elections looming in November.

Boehner said one of the biggest obstacles to immigration reform in the House was a concern that Obama would not fully enforce any laws that might be approved. As evidence of that, he accused him of changing "the healthcare law on a whim, whenever he likes".

On NBC's "Meet the Press" program, Senator Charles Schumer, a New York Democrat and one of chief architects of the Senate's bipartisan immigration plan, offered what he said was a simple solution.

"Let's enact the law this year but simply not let it actually start until 2017 after President Obama's term is over," he said.

"Now, I think the rap against him that he won't enforce the law is false. He's deported more people than any president but you could actually have the law start in 2017 without doing much violence to it."

Schumer said it would be difficult to pass immigration reform in 2015 or 2016 when the next presidential election season opens because Republican candidates would be staking out conservative positions on immigration in order to differentiate themselves from Democrats.

Senator Rob Portman, a Republican from Ohio who has been active on immigration, said "some Republicans would be interested" in Schumer's idea about delayed enactment, especially if there were measures to increase border security and prevent employers from hiring undocumented workers.

In June, the Senate passed a comprehensive bill that would provide a path to citizenship for those in the country illegally and tighten border security.

The bill stalled in the House, where many lawmakers oppose offering legal status for some 11 million people who live in the United States unlawfully.

(This version of the story is refiled to say Portman is a senator, not representative)