Hall, in the post for two years, has signaled that his office won’t soft-pedal the coverage assessments. If a health plan doesn’t have comprehensive benefits, it won’t count as coverage. Fearing a bad CBO “score,” Republicans facing backlash in their drive to gut Obamacare are turning the budget agency and its team of professional economic analysts into a punching bag as they try to discredit it.

President Donald Trump hasn’t directed any of his tweet fury — #FAKESCORES? — at Hall. But the White House press secretary has landed jabs.

“If you’re looking to the CBO for accuracy, you’re looking in the wrong place,” Sean Spicer said Wednesday at a briefing where the CBO came up repeatedly. “They were way, way off last time in every aspect of how they scored and projected Obamacare.”

Hall wouldn’t grant an interview. His predecessor, Democratic appointee Douglas Elmendorf, said roughly 40 people across different CBO divisions were involved in evaluating Obamacare’s impact. A former CBO staffer estimated that the number assessing the Republican American Health Care Act repeal bill is probably much smaller, about 10 or 15 people. CBO declined to comment.

Hall and former CBO directors have defended the office’s work as an unbiased view into how legislation affects the budget and overall economy, although the office has been dinged over its Obamacare estimates, which have undergone several revisions (some in response to changes the Republicans or courts made to the 2010 law such as making state Medicaid expansion optional). Yet Hall may end up being an unlikely hero for Democrats as they try to stop Republicans’ bill from becoming law.

The political limelight is not Hall’s natural milieu, and his professional history didn’t set him up to be a GOP foil. He’s a measured, conservative labor economist who worked at the White House Council of Economic Advisers and the Bureau of Labor Statistics under President George W. Bush. He also did a stint at the right-leaning Mercatus Center think tank.

Liberals were frosty when congressional Republicans — including Price, then chairman of the House Budget Committee — selected him to lead CBO in February 2015. He was on record as arguing that Obamacare was detrimental to the U.S. labor market, and also criticized proposals to raise the minimum wage.

“Based on Mr. Hall’s writings, it appears that we have very different views on a range of issues, and he would not have been my first choice,” Sen. Bernie Sanders said at the time. “His opposition to increasing the minimum wage and his resistance to sound strategies for eliminating poverty place him outside the mainstream.”

But Hall has sometimes surprised.

He was appointed to head CBO as Republicans in Congress revised rules for how the office would assess the impacts of legislation — a switch to what’s known as “dynamic scoring,” which lets CBO incorporate broader economic effects of proposed policy changes. Yet Hall’s use of that technique hasn’t always resulted in estimates that help the GOP agenda.

Notably, the CBO two years ago said fully repealing Obamacare would boost the federal deficit by $353 billion over 10 years. Even with “dynamic scoring,” the office still put the repeal price tag at $137 billion. That’s not the message Republicans were looking for as they attacked the law as money-guzzling big government.

And in one highly significant report in December — which set up the possible upcoming clash with the Republican Congress — Hall’s CBO said it wouldn’t count skimpy health plans as coverage in its scores. In other words, people with limited health care benefits that are unlikely to protect them against expensive or catastrophic medical events won’t meet the CBO standards for health coverage.

That means the CBO score of a Republican plan is almost certain to be less favorable than that of Obamacare.

“Members of Congress are often frustrated with CBO’s estimates of the effects of legislation because those estimates sometimes make it more difficult for those members to advance legislation they believe in,” said Elmendorf, who led the CBO from 2009 to 2015.

Under Elmendorf, the CBO also ruffled Democratic lawmakers’ feathers, in particular when it said the labor market would have 2 million fewer workers in 2025 because of the health care law. Republicans immediately used those findings to claim that Obamacare killed 2 million jobs.

Further back, a tough assessment — including a blunt statement about the expanded role of government in health care — by CBO Director Robert Reischauer in 1994 was one of many events that doomed the health reform initiative of President Bill Clinton and Hillary Clinton.

But Hall so far seems unperturbed by the repeal-and-replace fuss. Two former colleagues both described himj as “unflappable,” and noted that though he has free-market economic views, he’s never been partisan in any of his Washington roles.

“This is just a time when you need someone like Keith who is calm and steady,” said Charles Blahous, a senior research fellow at Mercatus and a former Social Security and Medicare trustee. “That doesn’t mean that CBO’s going to get everything perfect. But I think it would be very, very bad for the current debate if the CBO director were viewed as an advocate. Then you’d really have a problem.”

Benjamin Page, whose work for the CBO spanned from Reischauer in the 1990s to Hall and who is now at the Urban Institute, stressed the professionalism of his former colleagues, no matter who is running Congress.

“I can’t say enough about the analysts,” Page said. “People really care there about getting the answer right.”