Several conservative groups argued Thursday that a late-arriving score for the Senate Republican tax cut bill overestimated how much the national debt would grow under the bill, and said Republicans shouldn't hesitate to vote for the bill.

The Joint Committee on Taxation said the bill would add more than $1 trillion to the national debt over the next decade, even after agreeing that the cuts would lead to faster economic growth.

That finding left Republicans scrambling Thursday night to figure out a way to appease deficit hawks like Sen. Bob Corker, R-Tenn., Jeff Flake, R-Ariz., and Ron Johnson, R-Wisl, and forced the GOP to delay a vote on the bill until at least Friday.

But conservative groups said the JCT has it all wrong. As a start, some said it makes no sense for the committee to project less growth under the Senate bill, with its 20 percent corporate tax rate, than the amount of growth under the House bill, which called for a 25 percent corporate rate.

More specifically, some argued that the JCT has underestimated in the past how much tax cuts can actually help increase federal revenues due to increased growth. Freedom Partners said the same committee projected a revenue decline under the Bush tax cuts, although revenues actually grew.

"The Joint Committee on Taxation was off by nearly half a trillion dollars when projecting revenues from the Bush tax cuts," said James Davis, executive vice president of Freedom Partners. Davis said the JCT score shouldn't be counted on because the bill is likely to change before it passes.

"It's embarrassing that Republicans in the Senate are suddenly clinging to the findings of a half-finished analysis, based on flawed assumptions, delivered by a group with a historic track record of failure," he said.

The Tax Foundation agreed Thursday that the economic growth delivered by the bill was being underestimated, which led to an overestimation on the amount of new debt that would be created. For example, that group said the score "includes Federal Reserve activity that would counteract the economic expansion from tax cuts."

A spokesman for another group, Americans for Prosperity, said it would be watching to see if any senators use the score to delay a vote on the bill.

"Americans across the country who are expecting higher wages and more job opportunities are watching closely," said spokesman Levi Russell. "Our organization will not hesitate to hold those members of the Senate accountable who fail to deliver on the promise of real, pro-growth tax reform this year."