In the final hours before and after the bill passed, party leaders insisted that the tax plan would produce enough economic growth to pay for themselves with additional tax revenue from growing businesses and higher-paid workers. “I’m totally confident this is a revenue-neutral bill,” Senator Mitch McConnell of Kentucky, the majority leader, told reporters early Saturday morning after the vote, adding that he believed the bill would actually be a “revenue producer.”

Yet there was no data to support those claims, despite promises by the Trump administration that such an analysis would be forthcoming. The Treasury, whose secretary, Steven Mnuchin, has said repeatedly that his department was working on an analysis to show how the tax cuts would not add to the deficit, has not produced any studies that back up those claims. Last week, the Treasury’s inspector general said it was opening an inquiry into the department’s analysis of the tax plan.

The attack on the joint committee and its analysis is a change from the praise Republicans have long heaped on the body, which is staffed with economists and other career bureaucrats who analyze legislation in depth.

“The people who prepare our cost estimates are the best in the business, and they’ve been working on this issue for years,” Republicans on the House Budget Committee said on a page that was restored to the committee’s website on Monday afternoon, after what staff members said was an accidental deletion during a site redesign this year.

The critique is the latest example of Republican lawmakers muddying the waters on empirical research in an effort to boost their policy agendas. During the debate over repealing and replacing the Affordable Care Act, lawmakers lashed out preemptively at the Congressional Budget Office over how many people would lose health insurance.

At stake in the debate is more than the reputation of the economic analysts whose lifeblood is understanding the vagaries and intersections of the federal budget and tax code.

If Republicans are wrong and the joint committee is correct, the tax bill will add to an already worsening fiscal forecast in the United States. The federal government is already running an annual deficit of nearly $700 billion. The amount of federal debt has surpassed $20 trillion, and it is projected to grow by another $10 trillion over the next decade as government safety net spending rises because of retiring baby boomers and increasing health care costs.