Senate Majority Leader John Thune can afford to lose three Republican senators and still pass the bill, and there are more than that, right now, who have problems with it. Like the House, he will have to balance the concerns from moderate and conservative members of his conference.

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.

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.