WASHINGTON - Defense Secretary Mark Esper agreed on Tuesday to free up $3.6 billion from the Pentagon budget for President Donald Trump's border barrier by effectively defunding 127 military construction projects using emergency authorities.

Esper determined that the use of the military construction funds was necessary to support American forces deployed to the southern border with Mexico under the national emergency that Trump declared in mid-February. The formal determination allows Trump, under an obscure statute in the federal code overseeing the military, to tap the funds appropriated for other purposes without approval from Congress.

The Pentagon declined to release the list of 127 military construction projects that would be affected by the decision. Pentagon spokesman Jonathan Rath Hoffman said the list would be made available later this week, after the Defense Department finishes notifying lawmakers with affected projects in their districts and foreign embassies with affected projects in their countries.

During a briefing Tuesday, top Pentagon officials said the $3.6 billion will fund 175 miles of new or reconstructed barrier along the border with Mexico and help reduce the need for American troops on the border. Among the projects that the money will fund is a new barrier along the U.S. military's Barry M. Goldwater Bombing Range in Arizona, which abuts the border with Mexico, officials said.

The Pentagon will obtain the $3.6 billion by taking money away from 127 military construction projects that Congress already funded in recent years. About half of the $3.6 billion will come from projects within the United States and its territories; the other half will come from construction projects the U.S. military was planning to carry out in foreign countries.

The Pentagon said the projects weren't being canceled and wouldn't be delayed so long as Congress agreed to "backfill" the funds and once again appropriate money for the projects. Democrats have balked at the suggestion, noting that they have already funded the projects in question. They say the action flies in the face of Congress's constitutionally-mandated power of the purse.

There are about 3,000 active-duty troops and 2,000 national guardsmen serving on the U.S. border. Trump deployed them to free up the resources of U.S. Customs and Border Protection, which has been coping with large numbers of arrivals of primarily Central American migrant families.