Ryan argued in a meeting with Senate Republicans last month that the border adjustment tax would be necessary to raise $1.2 trillion to lower individual and corporate tax rates without adding to the federal deficit.

The budgetary impact of the tax package is crucial, because Senate Republicans plan to use special procedural rules known as reconciliation to pass it with a simple majority vote and avoid a Democratic filibuster. Legislation cannot add to the deficit outside the customary 10-year budget window and be eligible for this procedural protection.

But a growing number of Republicans have broken with Ryan on the border tax. They warn it will drive up the cost of imported products and American-made goods built with imported components.

Sen. John Boozman (R-Ark.), who is not a member of the Finance Committee, spoke for many members of the GOP conference when he said the border adjustment tax is going nowhere.