Senate Minority Leader Chuck Schumer (D-NY) said on Thursday evening that Secretary of Defense Jim Mattis could have sent in his resignation letter because he did not want to build President Donald Trump’s border wall.

“We all know that Secretary Mattis had real disagreements with the president on Syria and on the wall,” Schumer said. “Some have speculated that the president was going to demand that he start building the wall, which he knows he can’t do by law, and maybe that’s one of the reasons he stepped down.”

Earlier this week, Trump tweeted that the military will build the border if Democrats refuse to budge on giving him $5 billion to start construction on the border wall.

Trump tweeted: “Because of the tremendous dangers at the border, including large scale criminal and drug inflow, the United States military will build the wall!”

Mexico is paying (indirectly) for the Wall through the new USMCA, the replacement for NAFTA! Far more money coming to the U.S. Because of the tremendous dangers at the Border, including large scale criminal and drug inflow, the United States Military will build the Wall! — Donald J. Trump (@realDonaldTrump) December 19, 2018

Addressing Trump’s tweet, Pentagon spokesman Army Lt. Col. Jamie Davis reportedly said, “to date, there is no plan to build sections of the wall.”

“However, Congress has provided options under Title 10 U.S. Code that could permit the Defense Department to fund border barrier projects, such as in support of counter drug operations or national emergencies,” Davis reportedly added.

Schumer said Mattis is a “voice of stability in this administration” and added that there is “chaos in this administration.”

House Minority Leader Nancy Pelosi (D-CA) said she was “shaken” by Mattis’s resignation letter and said Trump administration officials leave in “dismay” or “disgrace.”