Republicans are gearing up for a fight with Washington's most respected budget wonk.

The Congressional Budget Office, the nonpartisan scorekeeping agency, is expected to release cost and coverage estimates for the American Health Care Act as soon as next week.

The coverage numbers aren't likely to be good — at least according to independent analyses from outside experts. And if the CBO analysis finds that the Republican plan will cover fewer people than Obamacare, Republicans are preparing to argue that the problem lies with CBO.

Several high-profile Republicans suggested Wednesday that they're already laying the groundwork to discredit the nonpartisan budget office:

White House press secretary Sean Spicer: "If you're looking at the CBO for accuracy, you're looking in the wrong place. They were way, way off last time in terms of how they scored and projected Obamacare."

"If you're looking at the CBO for accuracy, you're looking in the wrong place. They were way, way off last time in terms of how they scored and projected Obamacare." Energy and Commerce Chair Greg Walden (R-OR) : "If you go back to what CBO predicted would be covered on the exchanges today [under the ACA] they’re only off by only a two-to-one ratio."

"If you go back to what CBO predicted would be covered on the exchanges today [under the ACA] they’re only off by only a two-to-one ratio." Energy and Commerce health subcommittee chair Michael Burgess (R-TX): "The Congressional Budget Office score, while useful ... is hardly the final word on the issue."

"The Congressional Budget Office score, while useful ... is hardly the final word on the issue." Energy and Commerce Committee member Rep. Rick Hudson (R-NC): "The CBO number is a false argument the Democrats have created. They didn’t have support for their bill. This bill is going to save hundreds of millions of dollars.”

My colleague Jeff Stein has more on this from Capitol Hill, where he spent the day at the Energy and Commerce markup.

Walden is right: CBO initially overestimated how many people the Obamacare marketplaces would cover. But what they don't mention is that CBO also underestimated how many people Medicaid expansion would cover. The two have essentially offset each other. Obamacare is covering just about as many people as CBO expected back in 2013, before the expansion started.

But the problem isn't the scoring agency — it's the bill. Republicans are discrediting CBO presumably because they are worried about early estimates showing a significant drop in coverage. The ratings agency Standard & Poor's estimated Tuesday that 6 million to 10 million Americans will lose coverage under AHCA. One conservative economist thinks that's too low, and that the real number is more like 10 million to 15 million.

The reasons aren't complicated: The ACHA is significantly less generous than the Affordable Care Act. ACHA scales back the tax credits for the individual market by about one-third, and ends the Medicaid expansion in 2020. On the other hand, ACHA will almost certainly cost less than Obamacare, because the government won't be spending as much money on health insurance costs.

The problem is that this isn't what Republicans promised. Trump said his plan would cover "everybody." The CBO numbers will prove the ACHA doesn't. In January, a few days before he took office, President Trump gave an interview to the Washington Post where he said he would release a health care plan that "covers everybody." The moment the CBO numbers come out will be the moment his promise is discredited.

Kicking millions of Americans off health insurance isn't popular. The problem is that the CBO doesn't exist to make the politics palatable. Instead, it's making its best estimate of the bill's real-world consequences.

How accurate have the CBO's Obamacare numbers been, anyway?

Lucky for us, the Commonwealth Fund did a study on just that! In 2015 it compared CBO's enrollment estimates with other forecasts for the first year of Obamacare enrollment.

"CBO overestimated marketplace enrollment by 30 percent ... while it underestimated Medicaid enrollment by 14 percent," the Commonwealth Fund found. "Nonetheless, the CBO’s projections were closer to realized experience than were those of many other prominent forecasters."

Here is how CBO's projections stacked up against other forecasters in 2014:

CBO has generally overestimated marketplace enrollment — and underestimated Medicaid enrollment. You can see all of CBO's historical analyses of Obamacare right here.

Chart of the Day

President Trump and his threats of Obamacare repeal appear to have created something of a birth control boom. The health data firm AthenaHealth shows that IUD prescriptions this January have increased 30 percent compared with last year. Read more from Athena here.

Kliff's Notes

With research help from Caitlin Davis