(Bloomberg) -- Senate Republicans making one last-ditch effort to repeal Obamacare have the daunting task of assembling 50 votes for an emotionally charged bill with limited details on how it would work, what it would cost and how it would affect health coverage -- all in 12 days.

They need to act by Sept. 30 to use a fast-track procedure that prevents Democrats from blocking it, but the deadline doesn’t leave enough time to get a full analysis of the bill’s effects from the Congressional Budget Office. The measure would face parliamentary challenges that could force leaders to strip out provisions favored by conservatives. Several Republicans are still withholding their support or rejecting it outright.

And even if Republicans manage to get it through the Senate by Sept. 30, the House would have to accept it without changing a single comma.