(CNN) Former White House chief of staff John Kelly and the other four former secretaries of homeland security sent President Donald Trump and Congress a letter Wednesday calling for full department funding and an end to the month-long partial government shutdown.

"As former secretaries of the Department of Homeland Security (DHS), we write to you today with a simple message -- fund the critical mission of DHS," wrote the bipartisan group of Kelly, President George W. Bush alums Tom Ridge and Michael Chertoff, and President Barack Obama alums Janet Napolitano and Jeh Johnson.

Kelly, who left his White House role just as the shutdown began, derided the border wall at the center of the funding battle during an exit interview last month, telling the Los Angeles Times, "to be honest, it's not a wall."

Kelly continued at the time, "The president still says 'wall' — oftentimes frankly he'll say 'barrier' or 'fencing,' now he's tended toward steel slats. But we left a solid concrete wall early on in the administration, when we asked people what they needed and where they needed it."

In their letter Wednesday, the former secretaries cited the historical precedent of Congress prioritizing funding agencies such as the Department of Defense as a matter of national security.

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