WASHINGTON – Thirty minutes into an off-the-cuff defense of his decision to declare a national emergency to help build his border wall, President Donald Trump made an admission that may have handed ammunition to legal opponents of the move.

Trump, who has long described the situation on the Southwest border as a "crisis" and an "invasion," appeared to suggest his administration had all the time it needed to build the hundreds of miles of border barrier he has demanded for months.

"I could do the wall over a longer period of time. I didn't need to do this," Trump told reporters gathered in the White House Rose Garden on Friday, shortly before he signed a proclamation declaring the emergency. "But I'd rather do it much faster."

Trump’s opponents, including a number of groups and officials suing the administration over the national emergency, pounced on the president's candid remarks and said they appeared to undermine his claims of an urgent problem on the southern border.

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George Conway, an attorney and frequent Trump critic who is married to longtime Trump aide Kellyanne Conway, summed up the reaction in a post on Twitter: "This quote should be the first sentence of the first paragraph of every [lawsuit] filed."

A bevy of groups lining up to challenge Trump's national emergency are likely to rely on the quote to suggest the "emergency" is a fiction. Federal courts closely studied Trump's own words and tweets to pick apart the administration's argument that the travel ban the president signed in early 2017 wasn't targeted at mostly Muslim countries.But in a decision upholding the ban, the Supreme Court said it had to consider not only Trump's statements but also "the authority of the presidency itself" in reviewing his actions.

But experts said the president's words, which were emblazoned on cable network chyrons most of Friday, are unlikely to bring down Trump's emergency declaration. The National Emergencies Act gives a president wide authority to define what an emergency is – setting no hard rules over how urgent a problem must be or how potentially damaging.

Congress wrote the law, intentionally, to give presidents flexibility. The more challenging legal question for the White House is what powers Trump intends to invoke once the national emergency is declared.

"Because the president's words are so at odds with the ordinary meaning of 'emergency,' any brief challenging the emergency would be negligent not to quote him," said Peter M. Shane, a constitutional and administrative law professor at Ohio State University. "Whether a court would use those words to void the declaration is another matter."

Trump signed the proclamation Friday after Congress sent him legislation that funds the government through the end of September, averting another shutdown, and included $1.375 billion for the wall, much less than the $5.7 billion he had initially demanded. The White House said Trump will attempt to access another $6.6 billion through the national emergency and by shifting funds from other programs.

Public Citizen, a Washington-based watchdog group, was among the first to say they intended to sue over Trump's emergency. Allison M. Zieve, the director of the watchdog's litigation group, said the organization will "definitely recite his statement in our papers, and I expect that all the complaints will."

California Attorney General Xavier Becerra, a Democrat, also raised Trump's remarks during his own press conference on Friday in which he said he’s coordinating with other attorneys general to prepare a lawsuit.

"President Trump got one thing right this morning about his declaration when he said, 'I didn’t have to do this.' He’s right, he didn’t have to do this," Becerra said. "In fact, he can’t do this because the U.S. Constitution gives Congress, not the president, the power to direct dollars.”

U.S. government data from the southern border indicates the vast majority of narcotics captured at the border is coming in through ports of entry, not the wide swaths of border in between where additional barriers could be erected. And the number of migrants apprehended for trying to enter the U.S. illegally is significantly less than it was a decade ago.

Apprehensions along the southern border are actually at historic lows. Border Patrol routinely apprehended more than 1 million people a year – peaking at 1.6 million in 2000 – throughout the 1980s, 1990s and 2000s. In 2017, it apprehended just over 300,000. It 2018, it apprehended just under 400,000.

But experts predicted few of those points will matter legally.

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"The litigation isn’t going to turn on whether an emergency was 'necessary,'" said Stephen Vladeck, a University of Texas-Austin law professor who teaches national security law.

"It will certainly be invoked by challengers," he said, "but it’s not a game-ending blunder."

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Contributing: Richard Wolf, Alan Gomez