The Buzz is the Register’s weekly political news column.

With 31 challengers in Orange County’s four congressional districts currently held by Republicans, major endorsements offer a measure of who’s off to a good start — and help distinguish candidates in the bewilderingly vast field.

Political scientists often emphasize that endorsements don’t decide a race, that they’re less important than the size of a candidate’s campaign treasury in helping connect with voters. But major endorsements can be a signal to potential donors of a candidate’s legitimacy, as well as an indicator of the campaign’s networking, organization and alliances.

All four districts are considered vulnerable by national Democrats, who have targeted them as part of their strategy to flip the 24 seats necessary to take control of the House. Among the challengers, 24 are Democrats and the biggest threats to incumbents lie in their ranks. These Democrats are largely aligned on key issues, making personality, presentation and the ability to campaign critical to their eventual success.

As we can see from endorsements so far, early backers often reflect the candidates’ own political history and allegiances, their relationship to the Democratic establishment, and ethnic and gender affinities. Those with major endorsements are also among the top Democratic fundraisers in their districts.

District 39

Gil Cisneros, one of eight candidates challenging Rep. Ed Royce, R-Fullerton, has racked up one of the most impressive early endorsement lists of any Democrat in the county, with six current California members of Congress as well as former Rep. Loretta Sanchez, D-Santa Ana, lending their name to his effort. On Wednesday, he also announced the backing of the Congressional Hispanic Caucus PAC.

Cisneros, a Navy veteran, won a $266 million lottery in 2010 and used a large chunk of that money to launch a foundation that provided scholarships and other assistance to first-generation college students from impoverished neighborhoods. Part of that program has been an endowment to help pay salaries to congressional interns — a program that has won favor among Congress members. Cisneros, who recently moved into the district — to Yorba Linda — from Newport Beach, has also been endorsed by VoteVets and Giffords Courage to Fight Gun Violence.

Fellow Democratic challenger Sam Jammal is a former congressional chief of staff and a Commerce Department appointee under President Barack Obama. The Fullerton resident also worked on Obama’s campaign and spent time working for the Mexican American Legal Defense and Educational Fund. Endorsements include three Obama administration officials, a top Obama campaign official and civil rights icon Dolores Huerta. He also has the endorsement of three longshoreman union locals.

Among the four other Democrats in the race, pediatrician Mai Khanh Tran is backed by 314 Action, a science-based advocacy group, and two high-profile, pro-choice women’s groups, EMILY’s List and Feminist Majority. Tran also recently moved to Yorba Linda, leaving a Fountain Valley home that’s outside the district.

Democrat and businessman Andy Thorburn turned heads when he loaned his campaign $2 million — money campaign consultant Dave Jacobson said has since been shifting to an irrevocable self-contribution. His endorsements are somewhat lower profile: Assemblyman Reggie Jones-Sawyer, D-Los Angeles, a board president from a school dstrict — Ocean View — outside of the district, the International Union of Painters and Allied Trades District Council 36 and the United Steelworkers Los Angeles/Orange Counties. Thorburn lives in Villa Park, just outside of the district, but has said he plans to move into the district.

District 45

Of the seven Democrats challenging Rep. Mimi Walters in a district that reaches from Laguna Hills to Anaheim Hills, three have landed major-league endorsements so far.

UC Irvine law professor Katie Porter launched her campaign in April with the endorsements of Sen. Elizabeth Warren, a mentor since Porter was her student at Harvard, and Sen. Kamala Harris. She’s since picked up the backing of Rep. Lois Frankel, D-FL, EMILY’s List and the Feminist Majority.

Another Harvard-educated UC Irvine law professor, Dave Min, has been endorsed by Rep. Judy Chu, D-Monterey Park, and Fiona Ma, chairwoman of the state Board of Equalization.

Former U.S. Senate aide Kia Hamadanchy has been endorsed by two of his former bosses, Sen. Sherrod Brown, D-OH, and now-retired Sen. Tom Harkin, D-Iowa, as well as former Rep. Mike Honda, D-Walnut Grove. The son of Iranian immigrants has also been endorsed by the Iranian American Political Action Committee.

District 48

Seven Democrats are running against Rep. Dana Rohrabacher, R-Costa Mesa, with two cornering significant endorsements.

Hans Keirstead, a pioneering stem cell biologist from Laguna Niguel, has the backing of Democratic Reps. Jerry McNerney of Stockton and Bill Foster of Illinois, 314 Action and deep pocketed Democratic activist Wylie Aitken, who was a key figure behind Loretta Sanchez’s 1996 upset of Rep. Bob Dornan and is the former chairman of the well-heeled Democratic Foundation of Orange County.

Laguna Beach businessman Harley Rouda has the endorsements of former Bay Area Rep. Pete McCloskey, former state Attorney General Bill Lockyer and current Democratic Foundation Chairman Dan Jacobson. He’s also backed by former county Democratic Party Chairman Frank Barbaro and five area trade-union locals.

District 49

Retired Marine Col. Doug Applegate represents the avant garde of Democrats’ attacks on Orange County Republican incumbents this election cycle, coming within 0.6 percentage points of upsetting Rep. Darrell Issa, R-Vista, in the two-county district last year. This time around, the San Clemente attorney brings with him the endorsements of Sanchez, VoteVets, a host of local and state elected officials, two labor unions and seven union locals.

San Juan Capistrano’s Mike Levin, an environmental attorney and longtime Democratic activists, is backed by four Calfornia Congress members including the increasingly prominent Adam Schiff, state Controller Betty Yee, two San Diego City Council members, four union locals and a numerous local officials. In August, he became just the second congressional candidate this cycle to be endorsed by the National Organization of Women.

Rancho Santa Fe real estate investor Paul Kerr has the endorsments of San Diego Rep. Scott Peters and San Diego Councilman David Alvarez.