Two senators wrote Transportion Secretary Ray LaHood asking for an evaluation of the the "cash for clunkers" program before the Senate takes up a vote to extend the program's funding this week.

Sens. Dianne FeinsteinDianne FeinsteinTrump's Democratic tax dilemma Feinstein: Trump immigration policies 'cruel and arbitrary' The Memo: Could Trump’s hard line work on North Korea? MORE (D-Calif.) and Susan CollinsSusan CollinsOPINION: Congress should censure Trump for his unfit conduct No. 2 Senate Republican backs McConnell in Trump fight The fight to protect the Affordable Care Act isn’t over MORE (R-Maine), two principal authors of the initial bill, asked LaHood for key statistics on the number of cars purchased under the program, and the extent of the environmental impact expected to be gained by the program.

"We believe that Congress needs this information immediately in order to evaluate the program's effectiveness in attaining its two goals of stimulating automobile sales and reducing oil consumption," the senators wrote. "Without strong data on the effectiveness of the program, it will be more difficult for Congress to evaluate and improve the current program."

The extension of the program may face a bit more of an uphill climb in the Senate compared to the House, which easily passed the fast-tracked bill. Sen. John McCainJohn McCainBush biographer: Trump has moved the goalpost for civilized society White House to pressure McConnell on ObamaCare McCain: Trump needs to state difference between bigots and those fighting hate MORE (R-Ariz.), for instance, pledged to filibuster an extension.

(Hat tip: SenateUS)