In 2015, Rep. Ann Wagner, R-Mo., was one of few Republicans who stood and applauded when former President Barack Obama called for paid family leave during his State of the Union address.

“I can tell you at the time it was a pretty lonely place for a Republican to be,” she said. “But today we have a Republican White House willing to work with us on a conservative solution.”

Now Wagner is doing more than just applauding. She will soon have actual legislation ready to go. What she still doesn't have is much overt support from the Republican rank and file, and some outside conservative groups are mounting opposition to her plans. Instead, pro-paid leave Republicans threaten to open a rift within the party over its approach to family policy.

Many Republicans say they back some form of paid leave, but they're not coalescing around a specific plan, even though all acknowledge discussions are happening both behind closed doors and in open hearings. Much of that chatter has been helped along by the support of senior White House adviser and first daughter Ivanka Trump.

Sen. Marco Rubio, R-Fla., has taken the lead in the Senate, but failed to reach an agreement with other Republicans. Last week, he unveiled legislation that would allow parents to take out Social Security early following a birth or adoption in exchange for delaying retirement — but failed to get any co-sponsors.

“We’ve got some work to do,” Rubio acknowledged after unveiling his legislation, the Economic Security for New Parents Act. “I don’t think it’s disagreement on the goal.”

Wagner was by his side, and will introduce a House version when members return from the summer recess. She said there was “huge interest” in the lower chamber from GOP lawmakers but did not name names.

The plan has certain characteristics that could make it attractive to Republicans who would normally be skeptical of paid leave legislation. It is voluntary, for starters, and does not add taxes or new entitlement programs. Historically GOP lawmakers have been concerned that those factors, which are typical for Democratic paid leave plans, would limit employment, reduce wages, or backfire by causing fewer women to be hired or promoted.

Nevertheless, certain outside groups are raising the alarm about the plan. Most of all, they claim that it is a mistake to tap into Social Security, given that its trust funds are expected to run out in 2034. If that happens, beneficiaries would face an immediate cut of about a fifth of their benefits. Should a paid parental leave be carried out through Social Security, those benefits would be cut as well. The change would happen even sooner in the case of a recession.

“If Social Security was on a stable path and wasn’t going to go bankrupt, this proposal would probably work very well,” said Ben Gitis, director of labor market policy at the conservative American Action Forum.

Large changes to Social Security will be required to address the program’s finances. Trustees say that either benefits will need to be reduced by 17 percent or that the payroll tax will need to be increased by 2.78 percent, to 15.18 percent. Conservative groups have suggested additional measures, such as moving the age of retirement back or raising the cost of living adjustments.

“It would be a huge mistake to ask taxpayers to subsidize family leave benefits through Social Security, which is already drowning in red ink,” said Dave Abrams, spokesman for Freedom Partners, a free-market nonprofit associated with the Koch brothers. “Rather than creating a new entitlement program, Congress should modernize Social Security so it is affordable and sustainable.”

The conservative Heritage Foundation, a think tank that is influential among Republicans, also is opposed to the proposal, calling it a “problematic” way to provide access to paid family leave. Romina Boccia, deputy director at the organization’s Thomas A. Roe Institute for Economic Policy, said she was concerned private businesses would ditch the paid family leave provisions they have.

“I worry that if this proposal had any legs and were to become law, it would ultimately backfire on women of childbearing age,” she said. “Social Security is the wrong program to attach this to. Why stop at paid family leave? Why not allow it for other purposes like paying off student loans, or any other need for that matter?”

Instead, the organization supports ideas such as allowing workers to trade overtime for time off, something that is currently not allowed. Boccia said that years into the future, lawmakers would face political pressure to lift the retirement delay that had been used by new parents, particularly given the needs of people who work manual labor, such as home health aides or construction workers, and already have difficulty working until age 62.

Not all outside conservative organizations are opposed. The Independent Women’s Forum was the first to conceive of the Social Security plan, publishing a white paper of the proposal that laid the groundwork for the Rubio bill.

Carrie Lukas, the organization’s president, pointed out that some women have to drop out of the workforce because they are unable to access paid leave and then turn to government assistance, during which they are no longer paying into Social Security.

“At worst it’s neutral, or it’s possible that it will inch in the right direction,” Lukas said of the Social Security fund.

Andrew Biggs, a resident scholar on Social Security reform at the conservative American Enterprise Institute, made a similar point when testifying during a recent hearing.

President Trump has said he does not want to make any changes to Social Security's retirement program, but the White House has called paid family leave a priority.

“The White House looks forward to reviewing Sen. Rubio’s legislation, and all subsequent proposals, as we continue to work with members of Congress on both sides of the aisle to pass into law a national plan that will benefit America’s hard working families,” a senior White House official said.

Ivanka Trump said Thursday at a press event that other senators are planning to introduce their own legislation. She doesn’t think a bill will pass in this Congress, but said she was “cautiously optimistic” a bill could pass next year.

“At this point we are curating ideas with the hope to build consensus,” she said. “But it will take time.”

GOP Sens. Joni Ernst of Iowa and Mike Lee of Utah had been having discussions with Ivanka Trump and with Rubio, but are now signaling that they’ll be unveiling their own separate proposal, saying that they “intend to continue to work on a paid-leave proposal that we hope we can all support.”

“The fundamental idea of giving working parents the flexibility they need to make Social Security work for them so they can take time off to care for a new baby, is worth exploring,” they said in separately provided but identical statements. “Sen. Rubio and I just have some disagreements about the scope of that flexibility.”

Other GOP senators that have met with Ivanka Trump include Bill Cassidy of Louisiana and Deb Fischer of Nebraska. Senate Finance Committee Chairman Orrin Hatch, R-Utah, has been reviewing and analyzing the costs and benefits of wrapping paid family leave into Social Security, according to his spokeswoman, Julia Lawless.

So far, senators have not been vocal about the Social Security concerns raised by outside groups. Rubio said that the reason he was introducing the bill alone was because there were disagreements over whether parents should be able to transfer the leave benefit to a spouse, and whether both parents should be allowed to avail themselves of the benefit.

“It’s not even the framework of the proposal, but some of the details of it that other offices needed some time to get on board with or work through,” he said.

“We are prepared to invest the time and energy to do it,” Rubio said. “Big reforms require that.”