President Trump talks with reporters as he reviews border wall prototypes in San Diego on March 13. (Evan Vucci/AP)

Two powerful Democratic senators asserted Monday that the Pentagon has no power to reroute federal funding to President Trump’s prized border wall, after Trump began privately pressuring the military to delegate money toward construction of the barrier he had repeatedly promised during his 2016 campaign. 

Sens. Richard J. Durbin of Illinois and Jack Reed of Rhode Island wrote to Defense Secretary Jim Mattis on Monday, asking the Pentagon whether it believes it can transfer defense funding to Trump’s border wall. But the two Democrats made clear that they believe such a move would be illegal, while wasting money set aside for other, more pressing military needs. 

“Such a controversial move could only be funded by cutting other vital priorities for our service members, mere weeks after the Department communicated its needs to the Senate Defense Appropriations Subcommittee during omnibus appropriation negotiations,” Durbin and Reed wrote to Mattis

They added that after reviewing appropriations law, “we conclude that the Department of Defense has no legal authority, with or without a reprogramming request, to use appropriated funds for the construction of a border wall.” The Pentagon secured about $700 billion in the spending package that Trump reluctantly signed into law last month.

Durbin is the top Democrat on the Senate panel overseeing Pentagon funding, while Reed is the ranking Democrat on the Senate Armed Services Committee. 

The Washington Post reported last month on Trump’s conversations with advisers and with House Speaker Paul D. Ryan (R-Wis.) and detailed the president’s private suggestions that the Defense Department could fund the border wall by citing a “national security” risk.

But Congress maintains authority over how federal agencies spend money, and officials at the Pentagon have said that it cannot use its money for Trump’s border wall absent congressional action. 

Trump’s continued demand for border wall funds stems from the battle last month over funding the government, during which the administration secured $1.6 billion for his signature project. That is far less than the $25 billion the president sought, and it allowed only for “operationally effective designs” that had been already deployed as of last May.

The president was so incensed by the lack of funding for his border wall, among other issues with the omnibus spending measure, that he briefly threatened to veto the $1.3 trillion bill, which will keep federal government operations running until the end of the fiscal year on Sept. 30.