Sen. Tom Harkin (D-Iowa) has put a hold on Obama's Medicare nominee, Marilyn Tavenner. (Jonathan Ernst/Reuters)

The Senate Finance Committee unanimously supported her nomination. She has the support of multiple former Medicare heads; one compared her to Mother Teresa. Even House Majority Leader Eric Cantor (R-Va.), who does not like Obamacare one bit, really likes Marilyn Tavenner.

Enter, Sen. Tom Harkin, the Iowa Democrat who has put a hold on Tavenner's nomination.

Harkin is demanding, according to spokeswoman Katie Cyrul Frischmann, "An ongoing conversation about the future of the prevention fund."

That would be the health law's Prevention and Public Health Fund, which initially was a $15 billion trust fund dedicated to supporting public health and prevention activities.

Harkin has been the Prevention Fund's main advocate since it was part of the health reform debate. While the fund's appropriations dropped from $80 billion when it was initially proposed to $15 billion in the final version of Obamacare, that was still a significant commitment.

"The Senate's leading advocate for health promotion and disease prevention," John McDonough, former aide to the late-Sen. Ted Kennedy,  wrote of Harkin in 2010, "Is now in an enviable position to implement and advance this agenda."

Lately though, Harkin's position has seemed less enviable. Congress has cut away nearly $6 billion in funding to help keep doctor payments stable. The Center for Medicare and Medicaid Services, under Tavenner's leadership as acting administrator, has used another $454 million to help build the federal exchange.

Harkin has made no secret of his displeasure with this decision. “I helped to craft the Affordable Care Act and I want it to succeed as much as anyone," he said earlier this month of the administration's decision. "But I simply do not agree with the White House taking money out of prevention in order to implement the law."

How long will the hold last? Harkin's spokeswoman declined to comment. It's worth noting that Harkin isn't asking for the funds to be restored, but rather an "ongoing conversation" about the prevention fund. That's a bit easier for the administration to provide than millions—even billions—in new prevention funding ever would be.