WASHINGTON -- Veteran Republicans are flabbergasted that the Obama administration has not once budged during four months of talks in demanding nearly $2 billion to fight the Zika virus outbreak, a posture that's helped stall emergency legislation.

The White House and Democrats who participated in the talks say the sum, first requested in February, reflected what senior federal health officials determined is needed to track the spread of the disease, develop vaccines and study links between Zika and birth defects, among other tasks.

They blame Republicans for scuttling a Senate compromise last week, by inserting policy riders dealing with birth control and changing language in an unrelated part of the package concerning the flying of the Confederate flag.

Several senior Senate Appropriations Committee Republicans who served on a House-Senate conference panel that crafted the compromise, said they kept waiting for White House officials to give a little ground on the $1.9 billion demand.

They're still waiting. And the stakes were raised when a Florida hospital last week reported the fifth case of a U.S.-born baby with head deformities caused by Zika. The child was conceived in Haiti.

Asked if she is surprised that the White House continues to stick with its demands, Zika conferee Sen. Susan Collins replied: "I am, given the urgency of the situation and because the White House is not accepting the $1.1 billion, which the (Centers for Disease Control and Prevention) says is sufficient."

Accepting a $1.1 billion compromise "would get us started" in countering the mosquito-borne virus as summer temperatures in the South create perfect conditions for the insects that spread it, Collins said. "I'm puzzled by the White House's stance."

Sen. Lindsey Graham, R-S.C., expressed shock the White House hasn't budged, noting the $1.1. billion funding proposal received 81 votes in the Senate.

"It's an all-or-nothing White House," said Graham, who has been involved in several high-profile rounds of talks with the Obama administration on fiscal and budgetary matters. "I just think they must feel like it's good politics. ... They're just, to me, bitter going out the door."

Obama's top aides term the $1.1 billion funding level contained in a separate plan the Senate passed in May "woefully inadequate."

"Our public health professionals estimate that the federal government needs $1.9 billion of funding to attack this emergency," deputy spokesman Eric Schultz told reporters. "This bill falls far short of that.

"This is a bill that would also steal money from other critically important public health priorities, including those funded by the Affordable Care Act and those funded by our effort to combat Ebola," Schultz said. "So at the end of the day, this bill does not provide adequate funding."

Sen. Roy Blunt, R-Mo., a chief GOP negotiator during the bicameral Zika talks, said, "The White House needs to show some flexibility here."

Blunt, who has been a part of House and Senate GOP leadership for over a decade, offered the administration a civics lesson: "This is a government where the two houses of Congress and the White House have to agree on something. By definition, you can't wait until you get whatever you want if you're any of those three."

But Democrats, including one who was a Zika conferee, were quick to defend the White House.

"I agree with the administration that the amount of funding in aggregate is necessary for the research to prevent a spread of the virus, and the prevention activities," said Sen. Tammy Baldwin of Wisconsin.

She said "compromise is a good thing," but pinned most of the blame on Republicans for "the poison-pill riders that were added in the House," and the conference proposal's provisions that, as she said, would "cynically steal from other activities."

"If (funding) were the only issue, we'd be having a different conversation," Baldwin said. "But, regrettably, there are all those other issues."

And Sen. Claire McCaskill, D-Mo., said the administration is just "trying to move the number as close to what the health experts said we need as possible."

"If they said, 'We'll take $1.1 billion,' the House would have to say no because Obama asked for it," McCaskill said. "When it rains, it's Obama's fault," she said of House Republicans' thinking. She accused Republicans of "purposely" including the policy provisions to "kill the bill."

As lawmakers return after a July Fourth break, Senate Democrats are eager to reopen negotiations. But GOP members appear dug in over the birth control and Confederate flag issues, and the White House remains dug in on its funding level.

That's why one source, a former congressional committee aide who closely follows budget matters, said all indications are "there is no Plan B" on Zika.