Constitutional law professor Jonathan Turley issued a dire warning Thursday about the growth of executive power under President Obama, saying if left unchecked the U.S. president could "effectively become a government unto himself."

"It didn't begin with President Obama, but it certainly accelerated under President Obama ...and we are at a point that I consider quite dangerous," Turley told Fox News.

The George Washington University Law School professor spoke with Fox News a day after testifying before the House Judiciary Committee on the same topic. During the hearing, he warned that the nation is at a "constitutional tipping point" as the White House concentrates more and more power.

But he laid the blame at the feet of Congress as well, expressing shock that lawmakers have not fought back harder. "There's not been a whimper of regret or opposition of any substance coming from Congress," he said, adding: "To watch their power usurped by another branch, you would think would concentrate the minds of all members."

The president has been accused of inappropriately circumventing Congress on several occasions over the past few years, including by making unilateral changes to the implementation of the Affordable Care Act and by giving U.S. immigration officers leeway to ignore violations of U.S. immigration law.

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Turley said he actually agrees with some of those policies but nevertheless thinks the "means are wrong." He noted that some of these changes were made unilaterally after the president failed to convince Congress to approve them via legislation.

"It's not that President Obama is a dictator," he said. "I'm not questioning his motivations, what I'm questioning is his means."

Obama has vowed to use his "pen and phone" this year to accomplish some of his objectives. He has acknowledged he needs Congress for certain items, like comprehensive immigration reform, but claims he has the authority to act on his own in other areas.