Fox News senior judicial analyst Andrew Napolitano says President Donald Trump, contrary to what he's claimed, cannot use his emergency powers to bypass Congress and build his proposed border wall along the U.S.-Mexico border.

"The president may be biting off more than he can chew here legally and financially. He is clearly in dangerous waters constitutionally," he said.

Napolitano's statement was in reference to Trump's claim, during a press conference last week, that the White House "can call a national emergency" over the border wall dispute.

“We can call a national emergency over the security of our country, absolutely,” Trump told reporters in the Rose Garden. “Now, we can do it. I haven’t done it. I may do it, I may do it.”

Although the president does have emergency powers, "he can’t spend money and he can’t take property unless the Congress has authorized it,” Napolitano said. “That’s directly from the Constitution. If that were not the case, then President Obama could have declared, ’It’s a national emergency, there isn’t enough health insurance around, we’re going to start paying for it.'

"The president said he's threatening he will declare a national emergency to build that wall. Can he do that?" asked Fox Business host Maria Bartiromo.

To that, Napolitano gave his most concise answer yet:

"In a word, no. That's not me saying no, because the Supreme Court said no when Harry Truman attempted to do that. There was a steel strike during the Korean War, he asked the Congress to authorize him to seize the steel mills and operate them against the strikers' wishes and produce steel for our troops who desperately needed it during the Korean War. The Supreme Court said, 'No, you can't do that. Congress can do it. Congress can pay for the steel mills and operate them, but the president can't do it on his own.'

Stated differently, the Supreme Court has made it very clear, even in times of emergency, the president of the United States of America cannot spend money unless it has been authorized by the Congress."

Napolitano's comments come ahead of the president's prime time address on border security, during which he plans to declare a "National Security crisis" at the U.S.-Mexico border.

The president's claims have been debunked by former GOP Representative Carlos Curbelo (R-FL), who said that while both human trafficking and drug trafficking exist, they do not amount to a crisis.

"I visited the Southwest border in 2010 when I was working for United States Senator George Lemieux of Florida," he said. "There was a crisis back then. Things at the border have gotten a lot better over the last 12 years. We're seeing the number of people attempting to cross illegally drop dramatically, so no, I would not characterize this as a crisis."

Others have also weighed in, saying that the president's claims of a "crisis"––and a primetime slot––are largely an attempt to rile up his base.

In response to the president's request for airtime, House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer said in a joint statement that they should be given “equal airtime” to respond to whatever the president says.

“Now that the television networks have decided to air the President’s address, which if his past statements are any indication will be full of malice and misinformation, Democrats must immediately be given equal airtime,” Pelosi and Schumer said.