The Congressional Budget Office never exuded sex appeal, at least not until recently. Its bland office building, which sits unobtrusively by a freeway in southwest Washington, houses an often-overlooked assemblage of wonkish economists whose idea of professional happiness is producing 10-year fiscal forecasts.

Nevertheless, it’s an agency of indispensable importance that is now coming under attack not only from Critic-in-Chief Donald Trump but from a broad array of Republican leaders, including even Speaker Paul Ryan.

If, as Oscar Wilde said, that you can judge a man — or in this case an institution — by the quality of its enemies, then the C.B.O. has chosen very well.

The current Republican beef with the C.B.O. is that it has repeatedly (and undoubtedly correctly) concluded that conservative proposals to gut the Affordable Care Act would cost tens of millions of Americans their health insurance.