The mobilization of U.S. troops and the federalization of the National Guard "is a shared responsibility and needs to be done in cooperation between state, local, and federal authorities," said Dr. Meryl Chertoff, executive director of the Georgetown Project on State and Local Government Policy and Law.
"A unilateral effort," she said of Trump threatening to act alone, "is only going to be counterproductive."
There are instances in which presidents have mobilized U.S. forces without a governor's consent. President Eisenhower sent in the 101st Airborne Division to Little Rock, Arkansas, in 1957 to protect black students who were integrating into previously-all-white Central High School. Presidents Kennedy and Johnson subsequently invoked the law in the 1960s to enforce civil rights laws.
University of Texas law professor Steve Vladeck wrote for NBCNews.com that the president has "sweeping power" under the law "to use the military for domestic law enforcement" and does not need the consent of state governors to do so. Furthermore, the president can make "the factual determination that the military is necessary," Vladeck said.
Perez agreed that it is "unlikely" a court would overrule a sitting president on whether his factual determination of the need for federal forces was erroneous.
The law was last invoked by President George H.W. Bush during the 1992 riots in Los Angeles over the acquittal of police officers for assault in the beating of Rodney King. Then-governor of California Pete Wilson asked for federal troops to help quell the riots.
President George W. Bush considered sending federal troops to New Orleans to quell riots after Hurricane Katrina, but decided against it after the Louisiana governor said he did not want the military deployed.
Congress later amended the statute in the 2007 National Defense Authorization Act to liberalize the authority of the president to act without the consent of governors.
However, in the face of backlash by state governors, Congress subsequently withdrew that expansion of executive power, "indicating a congressional unwillingness to broaden the authority of the president to act unilaterally," Chertoff said.
Trump, she said, "hasn't given a good justification" for using the law, especially since he has not yet issued a proclamation but rather has simply used a "bunch of threats."
If U.S. troops are mobilized, or the National Guard is federalized, the action is also constrained by the Posse Comitatus Act of 1878, which says the troops must be used "in cooperation with police for peaceful purposes," Chertoff said.
(Story continues below)
Subscribe to our daily newsletter
At Catholic News Agency, our team is committed to reporting the truth with courage, integrity, and fidelity to our faith. We provide news about the Church and the world, as seen through the teachings of the Catholic Church. When you subscribe to the CNA UPDATE, we'll send you a daily email with links to the news you need and, occasionally, breaking news.
As part of this free service you may receive occasional offers from us at EWTN News and EWTN. We won't rent or sell your information, and you can unsubscribe at any time.
It is not to be equated with "martial law," a term that "doesn't really exist in U.S. jurisprudence," Perez said. The closest legal comparison might be the suspension of habeas corpus, which President Lincoln employed without congressional authorization during the Civil War.