Former CBO director Douglas Elmendorf AP Every single former director of the Congressional Budget Office signed onto a letter to Congress that called out some of the "recent attacks on the integrity and professionalism of the agency and on the agency’s role in the legislative process."

The CBO was created in 1974 as a way to provide Congress with nonpartisan analysis of proposed legislation.

In the past few weeks, the Trump administration has taken to attacking the CBO after the analysis office reported that the healthcare bill proposed by Republicans in the Senate would leave 22 million more Americans without insurance in 2026, compared to current law.

The former directors defended the office. "CBO's approach produces consistent comparisons of competing legislative proposals and unbiased projections of the impact of policy changes. Unfortunately, even nonpartisan and high-quality analysis cannot always generate accurate estimates," the eight former directors wrote in the letter.

The letter also comes just two days after the Department of Health and Human Services released a report on the Consumer Freedom Amendment proposed by Senator Ted Cruz that would allow insurance plans that don't comply with two regulations set up under the Affordable Care Act, the law better known as Obamacare: community rating and essential health benefits.

The HHS report took a look at what the amendment would do in the context of the ACA — not the BCRA bill. Consulting group McKinsey was contracted to produce the analysis, Politico reported.

The report came to the conclusion that Cruz's amendment would lower premiums in both the traditional ACA plans and the less regulated ones. That goes against what experts have said about the amendment in the context of the BCRA. Many say that it is likely premiums for both types of plans would likely rise if the amendment was put in place. The insurance industry's lobbying group said the amendment would lead to "widespread adverse selection and unstable health insurance markets."

On Thursday, the CBO scored an updated version of the bill, but that version didn't include the CFA, meaning the effects of that amendment have not been analyzed by the agency.

The former directors urged Congress to keep considering CBO analysis as part of crafting new legislation. "In sum, relying on CBO’s estimates in the legislative process has served the Congress — and the American people — very well during the past four decades," the directors wrote. "As the House and Senate consider potential policy changes this year and in the years ahead, we urge you to maintain and respect the Congress’s decades-long reliance on CBO’s estimates in developing and scoring bills."