Congressional Democrats will begin a futile bid to jam sweeping election reform through the Senate and alter its 60-vote legislative filibuster later Thursday when the House votes on a bill merging two separate voting measures.

The complex effort is certain to fail due to opposition by Sens. Joe Manchin (D-WV) and Kyrsten Sinema (D-Ariz.) to changing the filibuster rule — and a new memo from Senate Majority Leader Chuck Schumer (D-NY) suggests a promised showdown vote may not happen at all.

Democrats have opted to use an unrelated bill extending NASA’s property leasing authority as the vehicle to send both the John Lewis Voting Rights Act and the Freedom to Vote Act to the Senate.