A copy of a 2010 Census form. (Charlie Litchfield/Idaho Press-Tribune via Associated Press)

AS NEWS of one federal bureau director’s firing consumed Washington on Tuesday, another departure went mostly unnoticed: Census Bureau Director John H. Thompson resigned unexpectedly, a week after telling lawmakers in a hearing that the price tag on the 2020 decennial head count would be even higher than advertised.

Whatever the reason for Mr. Thompson’s early exit — his term expired in December, but he was expected to stay on through the end of the year — it is more bad news for an operation that was already in trouble. The Government Accountability Office added the 2020 Census to its annual list of high-risk federal areas in February, citing unreliable cost estimates and untested technologies, among other dangers. It is those IT systems that Mr. Thompson testified last week would be far more expensive than planned.

It is possible that new leadership could provide valuable new perspective to the Census Bureau. But Mr. Thompson’s departure and the instability that will follow it could not come at a worse time. The bureau must conduct a field test in spring 2018 to ensure its systems are up to snuff, and to do that it needs someone who can negotiate for fuller funding on the Hill. If Mr. Thompson had waited until winter to pack his bags, he could have led the charge. Now there will be no one: Selecting a nominee and shepherding him or her through confirmation could take months. Worse still, the deputy director post remains vacant.

The census plays an essential role in a fair and functional democracy by making sure communities get the right number of representatives in government — and that government builds schools and roads in the right places. The survey’s current woes are an entirely predictable, and predicted, result of congressional shortsightedness. Congress told the bureau it must spend no more on the 2020 operation than it spent in 2010 — $12.5 billion. With a bigger population to count, a better compensated workforce to pay and an outmoded pen-and-paper operation to reinvent, any director would have struggled with that mandate. It does not help that, so far this cycle, Congress has been funding the survey at historic lows.

President Trump must now step in, name a high-quality director and insist that Congress provide the Census Bureau the money it needs. The 2020 Census will begin in April of that year — right in the middle of primary season. The bureau’s troubles pre-date Mr. Trump’s ascension, but the census is happening on his watch. If it fails, he will own it.