Five years ago on Christmas Eve, when the Senate was about to vote on the Affordable Care Act, Kate Leone arrived to find a very crowded chamber. There was no place to stand on the floor, so Leone, who had spent countless hours working on the bill, sat next to her boss, then-Senate Majority Leader Harry Reid.

Reid, exhausted from last-minute negotiations and working one late night after another, accidentally voted no on the law he had spent so much time crafting. The room—full of people seated on the bench and along the walls—burst into laughter.

"He was super embarrassed," Leone says, recalling that day. "He was like, 'Can you believe I voted the wrong way?'"

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Leone, 43, remembers each step of the legislation's creation in detail because she was there for every one of them, from the time it left committee until it passed. Her involvement with Obamacare reflects her aptitude in health policy, something she's known for on the Hill.

"No one—no one—in Washington "¦ knows as much about health care as she does," Reid says. "They call and ask her what her ideas are. She is just the best."

He adds: "I get credit for having done something with that bill; she was involved in it every day. We spent days and days working on that, weeks and months."

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Leone began working on Obamacare in the fall of 2009 after the Senate Health, Education, Labor, and Pensions Committee and the Finance Committee had each produced a version of the bill. The two committee versions had key differences regarding Medicaid, exchanges, and in particular, a public option. The debate over health care reform made partisan splits even deeper, as President Obama attempted to push through the kind of policy other lawmakers had championed—to no avail—for decades.

Leone was tasked with merging the two committees' bills.

"I think Reid said, 'You have 10 days to do this,' and so we did. We got it done, and we worked a lot," Leone says. "We'd have these meetings with the White House and [Health and Human Services] people and Legislative Counsel and all the committee people sitting around this table, and we'd just go through the bill, line by line, making decisions about different things."

Leone didn't start her career working for politicians. She graduated from Columbia Law School in 1997 and clerked for two years. She then worked for two years as a lawyer on the health care task force in the antitrust division at the Justice Department, investigating violations of health laws. After that, she got a health policy job at the Democratic Policy Committee after Democrats took control of the Senate in 2001.

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Less than a year later, a health policy counsel position opened in Majority Leader Tom Daschle's office and Leone got the job. There, she worked on the Medicare Modernization Act, which produced what was at the time the largest overhaul of the program, and legislation protecting stem-cell research. After Daschle lost his reelection, Leone knew she wanted to work for Reid.

She started as his senior health counsel in late 2004. Since then, she's worked on high-profile deals like the Affordable Care Act and a recent human-trafficking bill that stalled the Senate confirmation of now-Attorney General Loretta Lynch.

"Kate Leone is one of a handful of staffers whom almost every senator in the caucus knows by name," says Bill Dauster, Reid's deputy chief of staff for policy. "She is one of a very few staffers who have addressed the caucus directly to explain the law."

Leone says that Reid is "the best boss you could ever have," and for reasons that have nothing to do with legislative work. Reid gives Leone the flexibility to care for her 7-year-old daughter—who was diagnosed with Lyme disease earlier this yearwhile fulfilling the requirements of her job.

"My daughter has sat in leadership meetings with the four leaders talking about stuff, like just sat there in the corner; they give her snacks," Leone says. "He'll be like, 'OK, Kate has to leave, her daughter's bored.'"

When National Journal asked Reid about his favorite memory of working with Leone, the senator didn't talk about the historical moments they've sat through together—he talked about her family.

"My favorite memories of Kate revolve around her and that little girl. Because the girl hasn't been healthy all the time, and Kate has—at my urging—always put that little girl first. Around here, I have no qualms with anyone who works here putting their family first," Reid said. "You asked me what my favorite memory I have of her— it's her taking care of that little girl."

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