Despite a setback last week, the outlines of a Republican health care bill that could pass the Senate are emerging. But senior Republican aides and strategists on and off Capitol Hill told FiveThirtyEight that they are not optimistic and that they see clear challenges with the bills path forward, largely because of differences between the partys more moderate wing and its conservatives.In a clear illustration of those tensions, Senate Republicans missed two self-imposed, informal deadlines last week. A scheduled vote on a motion to proceed to start the formal process of passing the bill was postponed after members said they would oppose even this procedural step. Then senators failed to reach an agreement on the bill that would have allowed the party to move forward. Majority Leader Mitch McConnell reportedly sent at least two draft bills to the Congressional Budget Office to have them scored at the end of last week, but thats only a partial step forward; Senate leaders routinely ask the CBO to score bills that will never be brought to the floor.