WASHINGTON -- The United States government is on the verge of shutting down over a dispute about subsidized pap smears, according to sources familiar with the budget negotiations.

The White House and Senate Democrats have publicly capitulated to ever-increasing Republican demands for spending cuts, but negotiations over the budget for the remainder of the fiscal year have shifted their focus from money to so-called riders -- provisions that restrict the federal government from spending money on certain projects or entities.

Riders are used by members of Congress to make social policy without going through the regular congressional committee process, or they are used to benefit business interests by specifically blocking the government from spending money to write or enforce certain regulations.

At a late-night White House meeting between the president and key congressional leaders, House Speaker John Boehner (R-Ohio) made clear that his conference would not approve funding for the government if any money were allowed to flow to Planned Parenthood through legislation known as Title X. "This comes down to women's health issues related to Title X," a person in the meeting told HuffPost.

The negotiations are dominated by men: All of the principal negotiators in both parties are male, as are most of the senior staff involved. (House Democrats, led by Minority Leader Nancy Pelosi (Calif.), have largely been left out of key talks.)

House Republicans have been insisting the roadblock to cutting a new budget deal is not just the culture-war riders attached to the spending plan, but a source familiar with a top-level White House meeting earlier Thursday said most of the discussion in fact was about the riders.

Senate Majority Leader Harry Reid (D-Nev.), House Speaker John Boehner (R-Ohio) and President Barack Obama met at 1 p.m., and while the discussion started with the numbers, a senior Democratic aide said it soon turned to non-budgetary provisions like defunding Planned Parenthood, Environmental Protection Agency rules -- and then some.

"They started talking about the money, but most of meeting was spent on the riders," a senior Democratic source said. "It wasn't just the top-line stuff. They got down into the smaller details and provisions -- things like mountaintop mining and other rules."

A similar dynamic played out late Thursday night in a meeting that led to no agreement.

Following the midday meeting, Senate Democrats met to chart a course forward and emerged united in opposition to any riders regarding Planned Parenthood -- which does not use federal funds to pay for abortions -- or the EPA.

"The riders that have nothing to do with deficit reduction have sort of taken over Boehner and the Republican Party," Sen. Charles Schumer (D-N.Y.) told reporters. "And unless they back off those riders, it's going to be impossible pretty much to avoid a shutdown. It's that simple."

Sen. Dick Durbin (D-Ill.), the number-two Democrat in the upper chamber, said that Boehner was under pressure on social issues not from the Tea Party, but from senior Republicans. "It's not about reducing the deficit. It's about hitting programs. He's gotta cut programs. And we think still we can reach agreement on the money. But he is under enormous pressure and he says it's not from the Tea Party, it's from the old guard, the Republican guard, that wants to once and for all show that they can force through some of these social issues, like abortion," Durbin told reporters Thursday evening in the Capitol. "The rider list gets longer and longer and non-negotiable."

A GOP aide confirmed Durbin's claim that it's the senior members who are insisting on riders. Polls show that the public is likely to blame the Tea Party for any shutdown, but ironically, most new members are more passionate about spending than social issues. Yet the public is likely to conflate the Tea Party with the culture wars if the government ultimately shuts down due to a dispute over funding for family planning.

"It's mostly a few older members who have seen an opportunity," said the GOP aide. "If you were to ask the freshmen individually, only a few would say this is all about the riders. And even amongst that smaller group, they would be split," with some focused on the EPA and others on restricting funds for health care.

"The true Tea Party guys in our conference are all about spending. That's it. Whatever the final deal is -- even if we got [the National Right to Life Committee] to score it -- we'd lose some guys because it didn't meet the full $100 billion," the aide added.

HuffPost spoke to a number of GOP freshmen, many of whom said they were more committed to funding cuts than policy riders. Although most voted for Republican-sponsored policy riders, some said they were willing to compromise as long as the final figure for cuts was large enough.

"My motivation is reducing the threat of the federal budget deficit, and I am flexible as to what gets cut so long as things get cut sufficient to avoid a federal government bankruptcy," Rep. Mo Brooks (R-Ala.) told HuffPost in March.

House Majority Leader Eric Cantor (R-Va.) said Thursday that the spending-cut difference between the two parties was minuscule. "If you look at the amount of money that we're actually talking about, in terms of the difference of where the White House is and where the House Republicans are, it's equal to maybe one penny of the entire federal budget," Cantor said at a press conference. "So that means that you can't find one penny to cut out of every dollar that the IRS spends? You can't find one penny out of every dollar that the post office spends? That's what we're talking about here."

Pelosi identified the distinction between the newer Tea Party members and the old guard weeks ago. "I had followed the debate very carefully on [the previous spending bill] and the 200 amendments. The newer members are about money, the more senior members are about riders," Pelosi said in mid-March.

A GOP leadership aide, however, told HuffPost that the culture wars were not the sticking point. "Spending, spending, spending -- that's the big issue," said the aide, adding that the GOP wanted more than $33 billion in cuts.

Either way, Democrats have no plans to defund Planned Parenthood at the insistence of House Republicans, Schumer said Thursday night. "We have been against them from the beginning and we're not changing, nor should we. These are fights that have nothing to do with the deficit," he said.

Schumer said earlier Thursday that Democrats were ready to meet Boehner's number, but that Boehner was using money as a distraction so that the public wouldn't realize his members were fighting over cultural issues.

"The only reason the numbers aren't solved is because Speaker Boehner knows that if he did that, then everyone would know that it's the riders, and he doesn't want that out. But if you look at how many hours in the rooms of negotiators that discussing riders, it's predominant," he said. "The Speaker's folks have admitted that we've been fair on the numbers."

"At one point we had an agreement on money, even though Boehner denies it," said Durbin. "It's hard to believe they would shut down the government because they can't get a vote on family planning and Planned Parenthood. Honest to goodness. Is that what the last election was about? I don't think so."

Cecile Richards, the president of Planned Parenthood, told HuffPost that the funding cut would be a threat to women's health. "We have three million come to us every year and two million come through some kind of federal program either for an annual pap or for birth control or for a breast exam or even prenatal care," she noted, adding that the cuts would disproportionately impact rural areas with relatively few medical options. "More than 70 percent of our health centers, more than 800 centers in the country, are located in rural America or communities that are medically underserved communities. That's what's getting lost here."

Conservative activists have long been pushing for cultural riders and, with Republicans back in control the House, have a chance to push them forward. "Why can't you slash Planned Parenthood and NPR and these -- these non-vital programs? Why can't you slash them?" Fox News host Bill O'Reilly demanded of Rep. Charlie Rangel (D-N.Y.) Thursday evening.

"Well, we're talking about health care. We're talking about education," Rangel replied.

"Health care is another matter," O'Reilly said. "That has to be taken very methodically because people's lives are affected. Nobody's life is affected by NPR. Nobody's life is affected by Planned Parenthood. These are options."

Mike McAuliff, Elise Foley, Laura Bassett and Amanda Terkel contributed reporting