House and Senate leaders are broadly aligned on the tax bill and have been meeting regularly to avoid points of conflict. But Senate Republicans made clear the compromise, a product of frenzied last-minute negotiations, must be negotiated again after it passed the House by a single vote on Thursday.

There are as many factions among Republicans in the upper chamber as in the House. Both chambers have to agree on the final product. It won’t be easy.

The Senate is poised to take up the Republican megabill after it narrowly passed in the House. But ongoing disputes and a slim majority mean more obstacles ahead.