Though not quite a proxy war, Democratic House Members are choosing sides and lining up with the two frontrunners to replace the late Rep. Juanita Millender-McDonald (D-Calif.) as the June 26 special election approaches.

State Sen. Jenny Oropeza (D) and state Assemblywoman Laura Richardson (D) have emerged as the top contenders in the crowded field vying to succeed Millender-McDonald in the overwhelmingly Democratic 37th district.

The demographics of voter turnout in this multi-ethnic, Long Beach-area seat are difficult to predict but could ultimately determine the winner.

“May the best grass-roots [campaign] win. That’s what happens in these low-turnout specials here,” said Alan Hoffenblum, a Los Angeles-based Republican consultant who is co-editor of the California Target Book.

The 37th district is 28 percent black and 23 percent Latino, with the remainder made up largely of whites and a small but significant portion of Asians.

In the Los Angeles Basin, blacks and Latinos tend to support candidates who share their ethnicity if given the option; Oropeza is Latina, and Richardson is black. Just how much that rule holds true — combined with the turnout level — could affect the outcome of the race.

As of Friday, 28,608 absentee ballots had been requested by voters, according to the Los Angeles County Registrar-Recorder’s office, and observers of the race say 40,000 might be the high-water mark for turnout.

At a Capitol Hill fundraiser Tuesday for Richardson, Rep. Maxine Waters (D-Calif.) appeared with the candidate, introducing her to various Members — some of whom brought checks with them, some of whom promised a contribution, and still others who said a contribution already had been made.

Among the Members in attendance were Democratic Reps. G.K. Butterfield (N.C.), Al Green (Texas) and Edolphus Towns (N.Y.).

Waters, who represents a Los Angeles-area district that is adjacent to the 37th, is considered the gold-standard for endorsements among black voters in that region of Southern California.

John Shallman, Richardson’s top strategist, called her the best cross-cultural candidate in the field, noting that in November 2006 she won with 60 percent of the vote a state Assembly district that is 14 percent black, 15 percent Latino, 10 percent Asian and nearly 60 percent white.

“Laura has a strong record of being a vote-getter across ethnic groups,” Shallman said. “We’re winning with [almost] every demographic, losing among Latinos by only 7 percentage points.”

Oropeza lists on her campaign Web site the endorsements of seven Members, including California Democratic Reps. Joe Baca, Xavier Becerra, Grace Napolitano, Lucille Roybal-Allard, Linda Sánchez, Loretta Sanchez and Hilda Solis.

On Saturday, the Richardson campaign released a poll that showed the Assemblywoman with a 9-point lead over Oropeza. In the survey, which was taken June 5-7 and has a 4.9-point error margin, Richardson was at 25 percent, Oropeza was at 16 percent, and Valerie McDonald (D) — Millender-McDonald’s daughter — was at 7 percent, with 35 percent undecided.

Oropeza’s chief strategist, Parke Skelton, dismissed the poll, implying its turnout model was flawed, and said the state Senator’s polling shows her with a mid-single-digit lead in two internal polls — the details of which he declined to disclose.

“The results we’ve seen are very different from what Richardson is shopping out there,” Skelton said. “The swing voters in this district are going to break heavily for Jenny.”

Shallman countered that he feels strongly that his turnout model is correct, saying he based it on those voters who have participated consistently over the past six election cycles.

Even if Richardson’s poll is accurate, one Democratic operative based in California cautioned that there still is plenty of time for Oropeza to surge.

Not only can the turnout model in special elections like this be hard to predict, but the late barrage of direct mail that is yet to come could influence the contest. Additionally, this operative said, if McDonald — who is black — makes any gains, Richardson likely would be the one who suffers.

“With these super-low turnout elections, either of the top-tier candidates can still make this a race,” this Democrat said.

If the ethnicity of the candidates has less of an impact on the race than some expect, it could be because one candidate’s major endorsements overpowers the key backers of the other.

Oropeza has been endorsed by the California Democratic Party and has a smattering of union support and the backing of key groups such as the National Organization for Women and the California League of Conservation Voters.

Richardson has been endorsed by some of organized labor’s biggest political players, including the California Federation of Labor, the Los Angeles County Federation of Labor — both of which are chapters of the AFL-CIO — and the Service Employees International Union. The L.A. County Federation of Labor in particular often has been the key to victory for many Democratic candidates running in area races.

“The county fed is investing hundreds of thousands of dollars in member-to-member communication,” Shallman said.

Skelton said the state Democratic Party was likely to carry more weight with average voters — while simultaneously offering Oropeza the support of the kind of party activists who knock on doors and man phone banks.

Skelton said the party’s backing — coupled with endorsements from the CLCV and NOW — will tend to influence the important voting bloc of white swing-voters, as the candidates are virtually identical when it comes to matters of policy.

“The party is a better endorsement in terms of what moves voters,” Skelton said.