Now that U.S. Sen. Barbara Boxer has made it official she will retire when her fourth term ends in early 2017, fellow Democrats are lining up to seek her job.

A Senate seat is a plum job anywhere, especially for Democrats in California, where it has been decades since any of them lost a reelection bid for statewide office. Whomever takes Ms. Boxer’s place can expect to become the state’s senior senator after 2018, when the then-85-year-old Dianne Feinstein is widely expected to retire.
 
Ambitious Democrats should beware: Their eagerness, even greed, could do in their party’s hold on Ms. Boxer’s spot. It has happened before in California, and very recently.
 
The field of potential Democratic candidates for Ms. Boxer’s slot is large, possibly going beyond obvious prospects like Lt. Gov. Gavin Newsom, state Atty. Gen. Kamala Harris, state Treasurer John Chiang, Los Angeles Mayor Garcetti and his predecessor Antonio Villaraigosa. Less obvious might be Silicon Valley moguls like Facebook chief executive Sheryl Sandberg and billionaire hedge fund operator Tom Steyer, of late a financial angel for liberal causes.
The Three Most Prestigious

They don’t all have to jump into the run to replace Ms. Boxer. Two years later, in 2018, Ms. Feinstein’s seat will most likely be available, along with the Gov. Brown’s office.
 
Heated competition for all three top jobs is likely. Friends say Mr. Newsom and Ms. Harris, longtime friends who share a campaign manager, probably won't run against each other.
 
They and the rest of the large possible field would be well advised to heed what happened in 2012 in the 31st Congressional District in San Bernardino County, where Democrats have a solid voter registration advantage, where President Obama twice won by healthy margins.
 
Mr. Obama, however, didn’t need to worry about the top two open primary system, where only the two leading primary election finishers make the fall runoff election.
 
In 2012, four Democrats went after this seat, which long had been held by Republican Gary Miller, who was expected to lose his job after redistricting in 2010 solidified the Democratic margin in his district.
 
The first complication for the Democrats was extremely low primary election turnout, because Mr. Obama had no primary election challenger and Republican Mitt Romney had sewed up his party’s nomination long before California voted in June.

Complicating Factors
 
Almost four times as many people voted in the November runoff that year as in the primary. This and the plethora of Democrats splintering their party’s vote allowed Mr. Miller and then state Sen. Bob Dutton to finish first and second in the primary. Democrat Pete Aguilar of Redlands, the preferred candidate of his party’s leaders, finished third with just 23 percent of the vote.
 
Democrats had to wait two years before Mr. Aguilar managed to win the seat last fall. If at least some Democratic prospects to succeed Ms. Boxer don’t stifle their ambitions, precisely the same thing could happen in the Senate primary, even though no Republican has yet expressed interest in running.
 
One thing for sure: If one and only one Republican makes this race, he or she is almost certain of a runoff slot. If a slew of Democrats gets in against two Republicans, both Republicans could advance to November, guaranteeing the GOP an improbable Senate seat for six years.
 
Look what happened just last spring, when Pepperdine University Prof. Pete Peterson was the only candidate with a GOP label running in a crowded field for secretary of state. Mr. Peterson, perhaps helped along by the federal indictment of San Francisco state Sen. Leland Yee, drew 30 percent of the vote despite being almost a complete unknown.
 
He then became a tough challenger for eventual winner Alex Padilla, another Democratic state senator at the time of the primary.
 
Some of the Democratic prospects will have to make an early choice to wait two more years before seeking higher office, or else the party could lose a seat it has held for decades. The wait could seem endless and frustrating to Democrats, who would have their own hubris to blame if they eventually lose the Ms. Boxer seat.
 
Mr. Elias may be contacted at tdelias@aol.com. He is the author of “The Most Promising Cancer Treatment and the Government’s Campaign to Squelch It,” now available in a soft cover fourth edition. For more Elias columns, visit www.californiafocus.net.