“A disease that destroys babies’ brains in utero is everyone’s worst nightmare — I’m not sure what could be much worse than that,” said Cindy Pellegrini, a senior vice president at March of Dimes, which is lobbying for the Zika funding. “But there doesn’t seem to be a sense of urgency on Capitol Hill.”

The Zika debate is caught up in election year politics and general GOP opposition to emergency spending. But there is another huge factor at play with Zika. Many congressional Republicans say they feel burned by the Obama administration’s response to the Ebola outbreak in 2014. In hindsight, the emergency response to that crisis was overfunded, they say, and now the White House is reluctant to reallocate all of the leftover money. Congress doesn’t want to give another blank check on Zika.

“Looked at what happened with Ebola — it looks like they asked for more than they needed,” said Sen. Richard Burr (R-N.C.), who backed the Senate’s $1.1 billion deal on Zika and is perhaps the most prominent Republican defender of public health and emergency preparedness.

The Obama administration and congressional Democrats say that by refusing to put up the money, Republicans are recklessly playing with fire on a health crisis that threatens the developing brains of fetuses.

“I listen to all of the really well-meaning people talking about the rights of the unborn and here we have a health crisis that dramatically impacts the unborn,” said Democratic Sen. Claire McCaskill of Missouri. “It seems to me we should be doing a much more aggressive job of making sure the resources that our health experts say that we need are in place.”

Already, there are 157 pregnant women in the continental United States and 122 in the U.S. territories — mostly Puerto Rico — with a confirmed Zika diagnosis who risk giving birth to babies with microcephaly, a birth defect where a baby’s head is unusually small and the brain is underdeveloped, according to a CDC report issued Friday.

President Barack Obama was briefed on Zika developments Friday and warned that the crisis is “something we need to take seriously.”

“This is not something where you can build a wall to prevent,” he said. “Congress needs to get me a bill. It needs to get me a bill that has sufficient funds to do the job.”

So far, all the cases in pregnant women in the continental United States involve women who traveled abroad or more rarely, who were infected by men who traveled to Zika hot spots. The virus is being transmitted locally by mosquitoes in the territories.

But public health experts expect that local transmission of the virus through mosquitoes will spread to the continental United States — mostly the Southern states — this summer.

“Zika is a big deal. It scares the heck out of me and all of us,” said Rep. Mario Diaz-Balart, a Republican whose South Florida district could face the brunt of the virus. “So we’re going to do whatever it takes. Having said that, we don’t want to do another ‘shovel-ready’ fiasco,” he said, referring to mismanaged projects funded by the 2009 stimulus package.

Obama administration officials say they’ve been trying to get ahead of Zika for three months, while a Republican-controlled Congress appears to slow-walk the process by asking for impossible details about how money will be spent on given weeks on a virus that public health experts are still trying to understand.

“Our initial understanding of this was that this was going to be treated as an emergency and that it would be funded that way,” said one administration official.

“There is, I think, a legitimate lack of understanding” about how emergency funding works among some House members, the official added. “What they’re asking us for … they’re not things that we would be able to answer.”

Those questions weren’t raised during the emergency responses to Ebola, the H1N1 virus or Avian flu, the official said.

The Obama administration says the Department of Health and Human Services and USAID need more cash to contain Zika’s spread here through mosquito control, to develop better tests and speed vaccine development and to expand Medicaid coverage in Puerto Rico, where heat, humidity and poverty make it ground zero for a U.S. outbreak.

Republicans want to see more funding set aside in the regular appropriations process to deal with crises. Burr accused the White House of underfunding emergency preparedness accounts in the regular budget process — funds that are supposed to be set each year to deal with crises like Zika.

Final approval of any kind of Zika funding appears unlikely to get to the president’s desk until next month at the earliest. But the timeline is tight: Congress leaves in mid-July and doesn’t return until September.

This week, the House voted to fund about one-third of the $1.9 billion request — an effort the White House considered so paltry it said it may veto it. And the Senate backed a $1.1 billion package attached to unrelated legislation.

Republican Sen. Roy Blunt of Missouri, the lead negotiator in the Senate, said he expects both chambers to pass stand-alone bills and move to conference.

“We’ll resolve this as quickly as we can but I would be surprised if it happens next week,” Blunt said Thursday.

But Congress is unlikely to approve the full amount the White House requested. For instance, Blunt said he has already eliminated $85 million the administration sought for building construction that is hardly an emergency. The construction request was in an earlier Zika proposal but has since been deleted, according to an administration official.

Many Republicans want the Zika money to sunset if the virus is contained and ensure that it can’t become a “slush fund” if money is left over.

A central point of disagreement is how quickly the money is needed.

The White House has already moved about $600 million in Ebola funding to Zika. Republicans say by the time that money is gone, or sooner, there will be an appropriation in the next fiscal year, which starts Oct. 1. The administration argues it needs the money as quickly as possible to get working on its response.

The two camps also don’t agree on whether the threat from Ebola has actually been eliminated. House Republicans say the Ebola outbreak is over so that funding can be moved. But the administration says that accomplishment is still tenuous, with occasional Ebola cases prompting a forceful response to prevent its spread.

About $1 billion in Ebola funds remain unspent. Less than $200 million of that hasn’t been allocated, according to the Obama administration.

About $500 million has already been allocated to a global health effort to help West Africa and dozens of other undeveloped countries shore up health care infrastructure to prevent another outbreak of Ebola or any other disease, according to an administration official. Congress specifically allocated that money to be spent over five years.

The unspent funding is also going toward tracking Ebola survivors — the virus could spread though semen for months after symptoms disappear — and preventing small flareups from spreading into another serious outbreak.

Last month, there were 13 Ebola cases and 1,700 vaccinations issued in Guinea and Liberia.

Sarah Wheaton contributed to this report.