The bill proposes a new $6,000 per-person tax deduction for seniors. The maximum deduction starts phasing down once income surpasses $75,000 per person, or $150,000 for joint filers. Then it phases out completely once income crosses $175,000 per person or $250,000 per couple.

Senate Republicans hope they are hours away from passing their massive tax and immigration bill. But the outcome is far from certain.