"There might be constituents who express concern".
The White House responded by attacking the CBO, saying it has a "history of inaccuracy".
The BCRA would cut Medicaid funding $772 billion by 2026, according to an analysis released this afternoon by the Congressional Budget Office (CBO). But, she said, "CBO analysis shows Senate bill won't do it".
Senator Rand Paul of Kentucky said it would be worse to "pass a bad bill than to pass no bill".
Several GOP senators said they wanted to see their bill cover more people than the House version.
The CBO said most of the savings in the Senate bill would come from spending cuts to Medicaid, with federal spending on the government health program for low-income and other vulnerable Americans declining by 26 percent in 2026 compared to current law.
"It's clear the CBO can not predict the purchasing patterns for millions of Americans", said Georgia Sen. Those ages are just shy of when people begin qualifying for Medicare coverage.More news: US, India Leaders Pledge to Boost Security, Trade Ties
The Senate bill would make financial assistance for premiums less generous than under the current law.
But the bill achieves that by pegging its supports to lower-cost, higher-deductible plans that offer less coverage rather than the middle-level plans Obamacare emphasizes - meaning more people will buy cheaper plans, and then have to pay more out of pocket when they do get sick. The overall net effect of the bill would be to reduce the budget deficit by $321 billion, while providing a cumulative tax cut of some $541 billion over the next decade alone, the vast majority of which would go to a small number of high-income households.
That's only slightly fewer uninsured than a version passed by the House in May.
The bill would also substantially reduce spending on Medicaid and reduce the value of tax credits that individuals use to buy health insurance, pricing many out of the market.
The measure is aimed at ending the obligation for people to get private healthcare insurance coverage or pay a fine, as occurs now under the reform sponsored by former President Barack Obama. In 2020 and beyond, the change in the risk pool, with older and poorer Americans most likely priced out, would bring these premiums down.
In yet another rebuke from outside Congress, the A.M.A., the nation's largest physicians organization, declared on Monday, "Medicine has long operated under the precept of primum non nocere, or 'first, do no harm.' The draft legislation violates that standard on many levels".
"I can not support a bill that's going to result in tens of millions of people losing their health insurance", Collins said. It would impose a 30 percent surcharge on premiums for people who have gone without insurance.