Obama's legislative chief stepping down
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Katie Beirne Fallon, the chief of President Obama’s legislative affairs operation, is leaving the White House, a major loss for the president’s team.

“Republicans and Democrats in Congress have their differences - but when it comes to Katie, they're united in their admiration and respect,” Obama said in a statement Friday.

“She came into her role at a time when we needed to build up our relationships with folks in both parties,” he added. “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.”

The White House’s current deputy director of legislative affairs, Amy Rosenbaum, will take over Fallon's post. Before joining the White House staff, she worked as an aide to House Minority Leader Nancy Pelosi (D-Calif.)

Obama said “there's nobody better prepared to step into this role" than Rosenbaum.

Fallon’s departure could complicate White House efforts to get Congress to pass the remaining items on Obama’s agenda during his final year in office.

It's also a reflection of the president's pared down to-do list for lawmakers, a bow to election-year gridlock and Republican control of both sides of Capitol Hill.

Fallon became a trusted adviser during her two years in the White House. The former aide to Sens. Harry Reid (D-Nev.) and Chuck Schumer (D-N.Y.) leveraged her ties to Capitol Hill to help Obama achieve victories on trade promotion authority, the Iran nuclear deal and a budget agreement last year.

Obama’s 2016 agenda is far less ambitious, but still includes two big-ticket items: the Trans-Pacific Partnership and an overhaul of the nation’s sentencing laws.

Fallon gave birth to twins last April and she told close friends and West Wing colleagues last year she was planning to stay through the end of 2015 to ensure passage of key items on the president’s agenda, according to a White House official. Her husband, Brian Fallon, is often on the road as a top spokesman for Hillary Clinton’s presidential campaign.

"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,” chief of staff Denis McDonoughDenis Richard McDonoughEx-Obama chief of staff: Obama's Russia response was 'watered down' Former Obama officials launch advocacy group aimed at Trump's foreign policy Obama: Bannon, Breitbart shifted media narrative in 'powerful direction' MORE said in a statement.

The president named Fallon his director of legislative affairs in 2013, following a tumultuous year that saw his efforts to pass comprehensive immigration reform and gun-control legislation stall in Congress.

Aides praised Fallon’s dogged work ethic. One official noted she went into labor while working at the White House and was escorted to the hospital by McDonough. Fallon participated in conference calls on the trade promotion authority bill while in the hospital after giving birth.

Reid, the Senate minority leader, said Friday that “none of the victories we secured in recent years would have been possible without her.”

“I have relied on her sharp insight, shrewd judgment and steadiness under pressure for years, first during her tenure here in the Senate and more recently in her roles with the administration,” he said in a statement.

Schumer called Fallon "the most popular staffer the administration has had" on Capitol Hil.

"Katie was the go to person when you wanted an open ear and the ability to get things done," he said.

Pelosi praised Fallon's successor, Rosenbaum, for her “depth of knowledge and integrity” in helping pass some of Obama’s biggest priorities, including his healthcare law.

"As she takes the helm of President Obama's legislative affairs team, I have full confidence that Amy will continue to drive vital progress for working families in the Congress,” she said in a statement. 

“Despite our political differences @Katie44 is one of the best people I've worked with. @WhiteHouse will miss her,” tweeted Mike Sommers, who served as chief of staff to former Speaker John Boehner (R-Ohio).  

This story was updated at 12:25 p.m.