The Trump administration and U.S. Customs and Border Protection (CBP) are going to ask for an appeal after a federal judge ruled Friday that President Trump's national emergency proclamation at the border is unlawful, acting CBP Commissioner Mark Morgan said Saturday.

The judge blocked a Trump administration rule that sought to strengthen the ability of federal officials to deny green cards to immigrants deemed likely to rely on government assistance -- the latest defeat in the courts for the administration's aggressive immigration policy.

ICE CHIEF WARNS COURT RULING BARRING DATABASE ACCESS ENDANGERS PUBLIC

Appearing on "Fox & Friends: Weekend" with host Pete Hegseth, Morgan said that they would "ask for a stay" so they can continue the construction of the wall that is "needed."

"I can promise the American people Monday morning that brand-new, big, beautiful wall is going to be continued to be built along the southwest border so border control can do their job," he told Hegseth."And, I'm still very confident that by the end of 2020, we're going to have that 450 miles of mission-critical wall that we need," he confidently stated.

At a fiery campaign rally in Louisiana on Friday, President Trump appeared frustrated with the court's decision.

"You know, we protect borders of other countries. We don't protect our own borders... In 15 minutes we could solve the problem," he told the crowd.

"As a law enforcement officer for many decades, Pete, I'm equally as frustrated as the president," said Morgan. "And, the American people should be worried as well."

Adding: "This is yet another example of judicial activism of a lower court that's absolutely impeding our ability as a law enforcement agency to safeguard this country against this humanitarian crisis and national security crisis. We're beyond frustrated."

"I have full confidence we're ultimately going to prevail," he said. "The wall is not going to stop being built. It's going to continue."

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Also on Friday, Acting Secretary of Homeland Security Kevin McAleenan stepped down from his post.

"Kevin now, after many years in Government, wants to spend more time with his family and go to the private sector," the president tweeted. "Congratulations Kevin, on a job well done!"

Morgan said he was sure it was a "hard decision" for the secretary, but that "we need to stay focused" because border-apprehension numbers are still at "crisis levels."

"We still have a heck of a lot of work to do to safeguard this country, so that's our focus," he concluded.

Fox News' Adam Shaw and Samuel Chamberlain contributed to this report.