Leon Panetta, Norman Mineta, Ron Dellums, Pete Stark, Howard Berman -- and now George Miller and Henry Waxman.

All powerful California Democrats first elected to the House of Representatives in the 1970s or early 1980s. They chaired committees on the budget, armed services, foreign affairs, education and labor, energy and commerce, and transportation, and the Ways and Means subcommittee on health.

They left for different reasons: Panetta and Mineta went on to run federal agencies; Dellums became a lobbyist before serving his failed term as Oakland's mayor; Stark lost to another Democrat when constituents and colleagues lost patience with him; and Berman lost when redistricting forced them to compete with another Democrat.

The Miller and Waxman departures are different -- and present new challenges to California Democrats.

They share ranking as the fifth most senior members of the House. They're not leaving for other jobs. Neither faced threats of viable election challenges. After 40 years, they've decided it's time.

Masters of policy and politics, Miller brought us landmark water and education laws while Waxman led Medicaid expansion and helped write the Affordable Care Act.

They talk about doing other things, about influencing policy from outside. But few believe that's all. Most ascribe their decisions to frustration being in the minority party of a House more polarized than at any time in memory.

"There isn't a lot of contact across the aisles and it's much harder for a minority party member to have an impact," notes Barbara Sinclair, a congressional scholar and UCLA political science professor emeritus.

As Waxman told the New York Times, "It's been frustrating because of the extremism of tea party Republicans. Nothing seems to be happening."

There's little sign that will change. Republicans will likely retain control of the House in this year's elections, and might even take the Senate. The GOP is so badly split internally that getting along with Democrats isn't a priority.

For California Democrats, Miller's and Waxman's departures mean loss of institutional knowledge and two of the nation's best political strategists and most-respected policymakers.

Nancy Pelosi, of course, remains minority leader, but with little hope of becoming speaker again in the foreseeable future. Maxine Waters tops Democrats on the Financial Services Committee and Sam Farr is the ranking member of an Appropriations Committee subcommittee. Anna Eshoo announced last week that she will vie to replace Waxman as ranking member of the Energy and Commerce Committee.

They must find ways to represent their districts and their state, and work with a Republican Party that shows little interest in working with them. It's a tall order.