Rep. John Larson (Conn.) has not yet officially assumed the title of Democratic Caucus chairman — a post he won uncontested last month — and already the job is shrinking.

The responsibility of looking after endangered incumbents, known as “member services,” is likely to get handed off to Rep. Chris Van Hollen (Md.), senior Democratic sources said. Van Hollen is gearing up for another turn leading the Democratic Congressional Campaign Committee but appears set to take on the portfolio under his new role as assistant to the Speaker.

The member outreach program was only added to the Caucus chairman’s profile two years ago as part of an agreement Rep. Rahm Emanuel (D-Ill.), then the incoming chairman, reached with Speaker Nancy Pelosi (D-Calif.) to beef up the post. And the decision to break the job off again represents the first concrete step Democratic leaders are taking to deal with his exit — and a recognition he will not be easily replaced.

A power center unto himself in the Caucus, Emanuel was a famously blunt, hard-driving force — a master strategist whose energy and ambition compelled him to take on both assigned and self-appointed roles that stretched his official status as the fourth-ranking Democrat in leadership. As he prepares to leave the chamber for a job as President-elect Barack Obama’s chief of staff, many Democrats are openly nervous about the impact of the one-man brain drain.

“These are really big shoes to fill, no question about it,” one Democratic chief of staff said.

After helping Democrats recapture the House in 2006 as DCCC chairman, Emanuel had been eyeing a run for Majority Whip. But he agreed to settle for an expanded Caucus chairmanship instead. Under the Chicago Democrat, the salary budget alone for the post roughly doubled to about $1.1 million annually, and it is not yet clear how much of Emanuel’s budget Larson will retain. A senior Democratic aide said Larson could pick up new duties for messaging or working with other members.

For Emanuel, the member services portfolio was an opportunity to continue mentoring the 42 Democrats he brought to the House. The role meant counseling them on the fundamentals of how to serve in Congress: everything from hiring staff to handling casework and drafting legislation.

Emanuel’s involvement ran deeper than frequent talks with the members themselves. He was often on hand on Monday mornings in the Cannon House Office Building Caucus Room for huddles that Jim Papa, his director of member services, held with freshman chiefs of staff to discuss the week ahead and help them troubleshoot.

Every three months, Emanuel and Van Hollen would sit down with lawmakers facing tough re-election battles to assess their standing and talk about the quarter ahead. By the most significant measure, the efforts paid off: Only four freshmen lost their re-election contests.

Now, with almost all of the 2006 class returning and a new crop of two dozen freshmen to look after, Van Hollen will have his work cut out for him. One senior Democratic aide said the Marylander was natural to take up the mantle. “He was the one who helped get these people elected at the DCCC, and he would be very good at it,” the aide said.

But talk persists that no one person can handle the task of keeping tabs on new and endangered Democrats — and that the leaders of caucus groups will need to step into the void.

Rep. Melissa Bean (D-Ill.), a home-state colleague of Emanuel’s who was recently elected into the leadership of the moderate New Democrat Coalition, said her group will “look out for those that are in the coalition and give them input on what’s worked for us and how to stay connected.”

Bean said that kind of cooperation was part of the system Emanuel helped build. “That’s the legacy,” she said.