Sen. Elizabeth Warren, D-Mass., and Rep. Beto O’Rourke, D-Texas, are teaming up to press Defense Secretary Jim Mattis for answers regarding the more than 5,000 troops who were sent to the southwest border in response to a caravan of thousands of migrants from Central America.

Warren and O’Rourke, who both are speculated to have 2020 presidential plans, along with Rep. Jackie Speier, D-Calif., the ranking member of the House Armed Services Military Personnel Subcommittee, referenced a New York Times report claiming that Pentagon officials consider the deployment, in accordance with an executive order from President Trump, as an “expensive waste of time and resources.”

“We are distressed by this report, and increasingly concerned about the lack of planning for and continued lack of clarity surrounding this operation, the lack of a clear mission for the deployed troops, the cost of this operation, and the appearance that the President is using the military for partisan political purposes,” the lawmakers wrote in a letter to Mattis on Monday.

“This is a disturbing report, and raises a number of questions as to whether or not the deployment of U.S. troops to the border by President Trump was a wise, effectively planned, and appropriate use of DOD resources,” they said.

In the letter, the lawmakers requested details concerning the cost and length of the operation, why active duty military personnel were deployed rather than the National Guard, what legal authorities were used to “justify this deployment,” and what are the “Rules of Engagement” for the operation. They also inquired if the operation will negatively impact military readiness overall.

Army Lt. Gen. Jeffrey Buchanan said Monday that the goal was to have all troops come home before Christmas, Politico first reported. "Our end date right now is 15 December, and I've got no indications from anybody that we'll go beyond that," said Buchanan, who is heading up the deployment.

But the Army followed up on Tuesday and said that “no specific timeline for redeployment has been determined.”

The lawmakers requested a response from Mattis by Dec. 10.