Add to this the fact that this vote _doesn't matter_ in the sense that deciding to turn it down isn't a final decision. This actually makes it easier for someone to vote against it for purposes of political expediency, knowing it won't affect the outcome as much. Voting in this meant much more jockeying for position.

As an irrelevant aside, I disagree with your present tense. Fractures are always existent within both Republican and Democratic parties; few congresses have been a matter of adding up the Ds and Rs except for on the few issues most bitterly fought over by D and R. In general these sub-divisions are the nature of the political beast.