The White House. (Carolyn Kaster/AP)

Even in a White House striving to be family friendly, there are limits.

President Obama announced Friday that his top legislative aide, Katie Beirne Fallon, is stepping down after two years in the post. Fallon, who helped improve his troubled interactions with congressional Republicans and helped broker deals on issues ranging from the budget to last year’s nuclear deal with Iran, had returned to work full time last August after having twin boys in the spring.

In a statement, Obama noted that Fallon had remained popular on Capitol Hill even at a time when partisan differences remain stark.

“Republicans and Democrats in Congress have their differences — but when it comes to Katie, they're united in their admiration and respect,” he said. “She came into her role at a time when we needed to build up our relationships with folks in both parties. And from bipartisan budget agreements, to protecting a deal that will prevent a nuclear Iran, to ensuring the long-stalled Ex-Im and IMF reforms were enacted, we simply could not have made the progress we've made without her.”

Fallon — who gave birth two months early, in April — had been juggling parenting and work as her husband, Brian Fallon, commuted back on weekends from Brooklyn as the press secretary for Hillary Clinton’s presidential campaign.

A White House official, who asked not to be identified in order to discuss personnel matters, said Fallon told close friends and colleagues in the White House last year that she was planning to stay until the end of 2015. Over the course of last year, Obama achieved several of his top legislative priorities, including approval of Trade Promotion Authority, the lifting of federal spending caps imposed through sequestration and the protection of the Affordable Care Act.

Sen. Charles E. Schumer (D-N.Y.), who used to be Fallon's boss, called her "probably the most popular staffer the administration has had. Katie is the total package and can see the whole field in terms of policy, press, and politics."

Senate Majority Leader Mitch McConnell's (R-Ky.) chief of staff, Sharon Soderstrom, was equally effusive: "Katie is a talented member of the president's team who will be missed by those she worked with on Capitol Hill. I appreciate both the professionalism and trust that we enjoyed."

The White House aide noted that the average tenure of a legislative affairs chief under Obama is about 18 months, given its grueling workload, and that Fallon appreciated the extent to which her colleagues helped accommodate her in recent months.

“She had a flexible schedule while they were still in the hospital managing to get conference calls and work on TPA done while spending the middle of the day at the hospital with her twins,” said the staffer, noting that after she went into labor while briefing White House Chief of Staff Denis McDonough, he personally escorted her to the hospital.

Fallon will be succeeded by Amy Rosenbaum, who serves as deputy director of legislative affairs and ran the office during Fallon’s maternity leave.

"Katie is a rare talent, capable of getting hard things done but never forgetting or compromising why we are doing those hard things: to make sure working families get the shots she got. We will miss her — I will miss her,” McDonough said in a statement. “Thankfully, her partner and our trusted colleague Amy Rosenbaum will lead the excellent team that she and Katie have built."

Rosenbaum, who joined the White House’s legislative team two years ago, spent nearly five years as policy director for then-Speaker of the House Nancy Pelosi (D-Calif.). In a statement, Pelosi said Rosenbaum “was a key force behind the development and legislative strategy that led to the enactment of the historic Affordable Care Act.”

"Amy has had a hand in some of the most consequential legislative progress for American families in the past decade,” Pelosi said. “Amy's strategic leadership helped craft the unparalleled productivity of the new Democratic Congress with our first 100 hours.”