If “repeal and replace” of the Affordable Care Act is Republicans’ job one, defunding Planned Parenthood is a close second.

In fact, the two priorities might be paired. House Speaker Paul Ryan, R-Wis., told reporters Jan. 5 that efforts to defund the organization “would be in our reconciliation bill,” referring to a measure Congress has put on a fast track aimed at repealing major pieces of the healthcare law.

But as Republicans are discovering that undoing the health law could be complicated, so, too, is separating the controversial reproductive healthcare provider from its federal funding. Efforts to hastily jettison Planned Parenthood from federal ledgers could actually jeopardize GOP efforts to repeal the health law.

One problem is that Planned Parenthood gets its funding from several different government sources. According to the group’s most recent annual report, covering 2015, Planned Parenthood affiliates, got $553.7 million from federal, state, and local governments, accounting for almost half of total funding.

According to the organization, about 75 percent of that government support comes from the Medicaid program to pay for direct medical services provided to low-income patients, including contraception, cancer screenings and sexually transmitted disease testing and treatment. The remaining quarter comes from other sources, primarily the Title X federal family planning program. The Congressional Budget Office (CBO) estimated last year that the group gets approximately $390 million annually from Medicaid and $60 million from Title X.

None of the funds from either program may be used for abortion, under longstanding federal prohibitions. Only half of the Planned Parenthood affiliates even offer abortion services, the group says. But it is still the largest single provider of the procedure in the nation, which has made it a target for anti-abortion lawmakers since the 1980s.

In recent years, one of the most ardent foes of the organization has been Vice President-elect Mike Pence. When he was a member of the House of Representatives, he led unsuccessful efforts to defund the program. As governor of Indiana, he was able to accomplish some of his goals. He also vowed to stop federal spending for Planned Parenthood during the campaign last fall.

Yet federal lawmakers have been stymied in these efforts.

One big reason is that taking away Planned Parenthood’s access to Medicaid funding would require a change in the federal law that guarantees most Medicaid patients with a choice to use any qualified provider. The Department of Health and Human Services has repeatedly warned states that have tried to evict Planned Parenthood from their Medicaid programs that they cannot legally do that because such a move would violate that law. Federal courts have consistently blocked states that have tried to end Planned Parenthood’s Medicaid funding.

Changing that section of Medicaid law likely would require 60 votes in the Senate to break a filibuster by Democrats. Republicans currently have 52 votes. The budget reconciliation bill, however, that is expected to be used to repeal portions of the health law operates under special rules. It cannot be filibustered and needs only 51 votes to pass.

That presents two problems for Republicans. According to CBO, permanently changing Medicaid law to make Planned Parenthood ineligible would cost, not save, money–approximately $130 million over 10 years. That is because, said CBO, taking away contraceptive access for some women would result in more pregnancies, and “additional births that would result from enacting such a bill would add to federal spending for Medicaid.”

That is not just theoretical. In 2013, Texas kicked Planned Parenthood out of its family planning program, and gave up its federal funding. The result was fewer women using birth control and more babies being born, according to an analysis published last March in The New England Journal of Medicine..

The second problem is political. While the House under GOP control has been strongly in favor of cutting off Planned Parenthood’s access to federal funds, there are a handful of Republican senators who oppose the idea. And a handful–three to be exact–is all it would take to threaten passage of the health law repeal effort.

“Obviously I’m not happy that the speaker has decided to include the defunding of Planned Parenthood—an extremely controversial issue—in the (budget reconciliation) package,” Sen. Susan Collins, R-Maine, told reporters on Jan. 5.

A spokeswoman for Sen. Lisa Murkowski, R-Alaska, said “she is concerned about defunding Planned Parenthood as she is a longtime supporter of Planned Parenthood and has opposed broadly defunding the organization.”

Collins and Murkowski fought against the inclusion of a one-year defunding of the organization in a 2015 health law repeal bill that President Barack Obama vetoed last January.

Although neither senator has said she would vote against the upcoming budget bill, if it includes the Planned Parenthood defunding, they join a growing list of Senate Republicans who in recent days have questioned the idea of repealing major portions of the health law before devising its replacement.

Meanwhile, eliminating Planned Parenthood’s access to funding under Title X also would likely be addressed in an appropriations spending bill. The current spending bill for the Department of Health and Human Services (and most of the rest of the government) expires April 28.

But rather than simply making Planned Parenthood ineligible, Republicans in the House have proposed doing away with the 45 year-old federal family planning funding and instead send the money to the nation’s network of Community Health Centers.

Last September, the Trump-Pence campaign released a letter to anti-abortion leaders vowing to defund Planned Parenthood “as long as they continue to perform abortions, and reallocating their funding to community health centers that provide comprehensive health care for women.”

At a CNN Town Hall Thursday night, Ryan expanded on that. “We don’t want to effectively commit taxpayer money to an organization providing abortions. But we want to make sure that people get their coverage. That’s why there’s no conflict by making sure these dollars go to federal community health centers.”

But that might not work either.

“For health centers, which currently serve about 25 million total patients, to have to absorb an additional 2 million people is totally impossible,” said Sara Rosenbaum, a health policy and law professor at George Washington University who looked at the issue in 2015.

In some areas of the country, Planned Parenthood and community health centers may not overlap. Planned Parenthood says in a fifth of the counties it serves, it is the only provider for low-income women. Asking community health centers to move into new areas, said Rosenbaum, “displays a fundamental misunderstanding of how long it takes a new provider to move into a potentially new community.”

According to the Guttmacher Institue, 83 percent of Black women who are at risk of unintended pregnancy currently use a contraceptive method, compared with 91 percent of their Hispanic and White peers, and 90 percent of their Asian peers.

Despite the difficulties, however, the shifts in political control this year leaves Planned Parenthood concerned about its future.

While the organization has weathered funding threats before, “it is very true when you have people like Mike Pence and Paul Ryan, who have been laser focused for years (on ending funding), that they will make it a very high priority,” said Mary Alice Carter, Planned Parenthood’s vice president for communications.

She said the organization is counting on the 2.5 million patients it serves every year to make sure their elected officials know they oppose the defunding effort. Whether that will be enough remains unclear.

Kaiser Health News contributed to this story.