“Let’s face it, he was central,” said Sen. Bob Corker (R-Tenn.), who negotiated a crucial budget agreement with Toomey that paved the way for the tax bill. “This would be, I’m sure, the ultimate thing for him to accomplish here in United States Senate, and so he stayed focused.”

More broadly, Toomey’s influence represents the imprint of the supply-side doctrine in the bill — the notion that the benefit of lower taxes and fewer regulations on businesses and investors, in the words of its critics, “trickle down” to other Americans. That thinking delivered most of the dollar value of the GOP tax cuts to a lower corporate rate and a new break for owners of “pass through” businesses, whose profits are taxed as individual income, while offering relatively meager benefits for wage-earning Americans.

“But for Pat Toomey, it’s not likely we would have seen 50-plus votes in the Senate for that nature of a tax cut,” said David M. McIntosh, president of the Club for Growth, a group Toomey led before entering the Senate.