Sometime in the next few days the Congressional Budget Office will release its analysis of the latest version of the Republican health care plan. Senator Mitch McConnell is doing all he can to prevent a full assessment, for example by trying to keep the C.B.O. from scoring the Cruz provision, which would let insurers discriminate against people with pre-existing conditions. Nonetheless, everyone expects a grim prognosis.

As a result, White House aides are already attacking the C.B.O.’s credibility, announcing in advance that whatever it says will be “fake news.” So why should we believe the budget office, not the Trump administration? Let me count the ways.

First, this White House already has a record of constant, blatant lying about health care that is, as far as I can tell, without precedent in modern history. Just a few days ago, for example, Vice President Mike Pence made the completely false assertion that Ohio’s expansion of Medicaid led to a cutback in aid for the disabled — a lie that the state’s government had already refuted. On Sunday, Tom Price, the secretary of Health and Human Services, claimed that the Senate bill would cover more people than current law — another blatant lie. (You can’t cut hundreds of billions from Medicaid and insurance subsidies and expect coverage to grow!)

The point is that on this issue (and others, of course), the Trump administration and its allies have negative credibility: If they say something, the default assumption should be that they’re lying.