Mr. Obama conceded that without new legislation, his action — which includes de facto amnesty for more than 4 million illegal immigrants — technically could be undone rather easily. But in practical terms, the president said his successor will be unable to roll back his executive moves because doing so would carry grave political consequences. His comments underscore the White House’s belief that the executive action, while lacking the heft of actual law, still can permanently transform the way America deals with illegal immigration.

“It’s true a future administration might try to reverse some of our policies. But I’ll be honest with you — the American people basically have a good heart and want to treat people fairly and every survey shows that if, in fact, somebody has come out and subjected themselves to a background check, registered, paid their taxes, the American people support allowing them to stay. So any future administration that tried to punish people for doing the right thing, I think, would not have the support of the American people,” Mr. Obama told a supportive crowd at a town hall meeting in Nashville. “It’s true, theoretically, a future administration could do something that I think would be very damaging. It’s not likely, politically, that they reverse everything we’ve done.”

Mr. Obama’s confident declaration comes amid a growing backlash in Washington and across the country after last month’s long-awaited executive action.

ME the President

While blaming congressional Republicans for blocking a comprehensive immigration reform bill, the president granted amnesty to more than 4 million illegal immigrants, freeing them from the threat of deportation and allowing them to legally compete for jobs.

GOP lawmakers have vowed to fight the action in court, as have at least 18 states, which already have sued the president over the issue.

Republican lawmakers argue Mr. Obama’s action puts law-abiding Americans at a significant disadvantage at a time when the economy remains fragile.

“More than 200,000 Tennesseans remain out of work, but rather than prioritize their plight, the president is putting the interests of those who have broken our laws ahead of them. Why should unemployed Tennesseans have to compete with illegal immigrants for jobs? And why should those who break our laws to come here be rewarded while so many wait to come here legally? This is wrong and the President does not have the authority to change our immigration laws without Congress,” said Rep. Diane Black, Tennessee Republican. “The Obama Presidency has been a disaster and can’t end soon enough. But in the meantime, I will work with my colleagues in Congress to fight the President’s unconstitutional power grab.”

But the president pushed back against that criticism, too, charging that Ms. Black and others who claim illegal immigrants will put American citizens out of a job have already been proven wrong by history.

“I understand those concerns, but as I said, they’re not new. We’ve had these concerns since the Irish and Italians and Poles were coming to Boston and New York,” he said. “But what our history and the facts show is, generation after generation, immigrants have been a net plus to our economy and a net plus to our society.”

Mr. Obama went on to cast himself as something of a moderate on immigration reform, saying that, behind the scenes, he’s fought against those who believe the U.S.-Mexico border should be erased entirely.

“There have been times, honestly, I’ve had arguments with immigration rights activists who say, effectively, ‘There shouldn’t be any rules. These are good people. Why should we have any enforcement like this?’ My response is, ‘In the eyes of God, everybody is equal … I don’t make any claims my child is superior to anybody else’s child. But I’m the president of the United States, and nation states have borders,’” the president said. “If we had no system of enforcing our borders and our laws, I promise you, everybody would try to come here.”