An Aedes aegypti mosquito on a human. (Luis Robayo/Agence France-Presse via Getty Images)

CONGRESS AND President Obama are engaged in a needless spat over the president’s Feb. 8 request for about $1.9 billion to fight the growing danger of the Zika virus. For two months, the Republican-controlled House and Senate have not acted. Further delay will degrade preparedness for a virus that carries a greater punch than was first believed . The dispute is one that White House and legislative staff could easily resolve in an hour — and ought to get done tomorrow.

The Centers for Disease Control and Prevention announced April 13 that a careful study showed Zika is a cause of microcephaly and other severe fetal brain defects. Tom Frieden, the CDC director, said the study was a “turning point.” This means that women who are pregnant and get infected by the mosquito-borne virus are at risk of giving birth to children with the brain disorder, although not every pregnant woman infected will do so. The virus, carried by Aedes mosquitoes, has been steadily expanding throughout the Americas in recent months. So far, the 358 cases in the United States have been among travelers, but local outbreaks could reach the shores of the southern United States this summer. In many cases, the virus causes mild symptoms, but the link with brain damage is now of genuine concern, especially in poor, urban areas.

When infectious disease strikes, it often races ahead of the response by people. It has been an unfulfilled dream of biomedical researchers to find a rapid response mechanism, but vaccines and therapeutics take time to discover and manufacture. The scientific and medical hurdles aside, another reason for delay is that governments wait too long. This was a central lesson of the Ebola disaster in West Africa. It is not known how serious of a Zika crisis could erupt in the United States, but the time to prepare is now. A multipronged effort is urgent: research on vaccines and rapid diagnostics; bolstering the nation’s fragmented mosquito control programs; and public education, among other things.

Presented with White House requests for the open-ended emergency supplemental, Republicans balked, suggesting that Mr. Obama could use unspent Ebola funds instead. Mr. Obama agreed April 6 to redirect $589 million in Ebola money for Zika response, but he insists his original request is still valid. House Republicans are saying that the White House hasn’t provided enough detail. We applaud the congressional urge to apply oversight, but not the delay. Congress and the president have no shortage of staff to investigate, hammer out legislation, create programs and build an effective response. They must get to work immediately. Zika doesn’t know a Democrat from a Republican.

What will members of Congress tell those mothers and children in the United States who become victims of Zika this year and next year because resources were not committed to preparing for the virus? That there were “unanswered questions” in the paperwork? How lame, and irresponsible.