Senate leadership, who had hoped to vote to pass the $1.5 trillion tax bill by late Thursday night, instead sent lawmakers home and began to search for a new way to offset the cost of the legislation. They are looking to win the support of several senators, including Bob Corker (R-Tenn.), who has led a small group of colleagues in demanding that the bill not drive up the nation’s debt.

Now, Republican leaders may have to brace for an intraparty battle over how far to go to accommodate deficit concerns. Other Republicans are arguing strongly against reducing the size of the bill’s tax cut, as may now be necessary to satisfy the deficit hawks.

The new tension threatens to undercut what had been an unusual degree of unity within the GOP, with even Sen. John McCain, the Arizona Republican who has repeatedly defied his party, announcing support for the bill Thursday.