The lawmakers attracting the most concern from leadership and the White House are Sen. Ron Johnson (R-Wis.) and Steve Daines (R-Mont.), who say the current version of the bill favors corporations over other businesses.

There are numerous members demanding changes, and their desires don’t all overlap. Together, the requests put Republican leaders in a difficult position, as they attempt to accommodate individual holdouts on a one-off basis without losing other members or creating a situation in which the bill collapses under the weight of disparate demands.

Adding to the leaders’ difficulty, the total size of the tax plan cannot be more than $1.5 trillion over a decade, so adding new benefits could force Republicans to find ways to raise additional revenue. Presently, they only have roughly $80 billion in wiggle room to use, a small sum because many of the changes would be spread out over 10 years.