The decision by Rep. George Miller (D-Calif.) to retire after this year adds him to a fast-growing list of lawmakers who are opting not to run again for office. His decision not only further depletes the ranks of liberal Democrats in the House, but also robs House Minority Leader Nancy Pelosi (D-Calif.) of one of her closest friends and top lieutenants.

House Minority Leader Nancy Pelosi (D-Calif.), center, flanked by top leadership lieutenants, on Capitol Hill in 2009. (AP)

That got us thinking: Who besides Miller is still within Pelosi's close inner circle these days? Based on conversations with her closest aides, she still relies on a small clutch of members that she's served with for decades, most of whom hail from her home state of California and who are veteran members of the House Appropriations Committee -- which Pelosi served on before climbing House leadership ranks -- or senior members of other key committees.

Here's a quick glance at some of the House lawmakers Pelosi is most likely to call upon to champion a specific cause, help manage the House Democratic Caucus, or spend time with after hours.

* Rep. George Miller (D-Calif.): He's the first among Pelosi's close friends and lieutenants. First elected to Congress in 1974 at the age of 29, he's one of the last remaining members of the "Watergate babies" class of 1974, which was elected to Congress in the wake of the Nixon Watergate scandal. In the decades since, Miller has been a liberal champion of some of the marquee Democratic legislative accomplishments of the last several decades. He worked with Republicans on the "No Child Left Behind Act," held the first hearing on the Lilly Ledbetter Fair Pay Act and help author the economic stimulus bill passed in 2009. Miller now serves as the ranking member on the House Education and the Workforce Committee and naturally serves as a key Pelosi ally on health, education, labor and economic issues.

* House Minority Whip Steny Hoyer (D-Md.): Their rivalry is well-documented and they occasionally end up on either side of a major issue (last month's vote on the bipartisan budget agreement is the most recent example), but she still works well and closely with the second-ranking Democrat, according to aides. Their relationship dates back to the 1960s, when they both worked for Sen. Daniel Brewster (D-Md.).

* Reps. James Clyburn (D-S.C.) and Xavier Becerra (D-Calif.): The third- and fourth-ranking House Democrats, they're also key leadership lieutenants. Each embodies one of the traits mentioned above: Clyburn is a long-serving member and the Democratic leadership team's liaison to the Appropriations Committee, while Becerra is yet another Californian in Pelosi's orbit. Becerra also was Pelosi's closest link to the bipartisan "Group of Eight" talks on immigration reform that have stalled in recent months.

* Reps. Nita Lowey (D-N.Y.) and Rosa DeLauro (D-Conn.): Lowey is the senior Democrat on the House Appropriations Committee and thus close to Pelosi on spending matters. DeLauro also is a longtime appropriator and a fierce defender of federal health and education programs and a close Pelosi friend.

* Reps. Anna Eshoo (D-Calif.), Barbara Lee (D-Calif.) and Zoe Lofgren (D-Calif.): Eshoo is Pelosi's closest House colleague/friend from California, while Lee and Lofgren are two other long-serving Californians. Lee, one of the chamber's most liberal members, is a senior member of the Appropriations and Budget committees, while Lofgren is a senior member on the House Judiciary Committee and also was part of the "Group of Eight" immigration talks.

* Rep. Steve Israel (D-N.Y.): Seen by many Democrats as one of several potential candidates for Speaker if Democrats ever retake the House and Pelosi decides to step aside, he's a more recent addition to Pelosi's close circle of advisers and her go-to guy on all things 2014 in his role as head of the Democratic Congressional Campaign Committee.

* Rep. Chris Van Hollen (D-Md.): Another might-be Speaker candidate, he's a key lieutenant on economic and budgetary matters, especially since becoming the ranking Democrat on the House Budget Committee.

* Sen. Barbara Boxer (D-Calif.): One of her closest friends on Capitol Hill who's not in the House, the senator is one of the folks Pelosi spends time with when they're not on the clock, aides said.