LOS ANGELES (AP) — Members of Congress are facing a new reality in California: competitive elections.

For years, political deal-making in the nation's most populous state produced congressional districts that virtually guaranteed one-sided results on Election Day. Even during a period of widespread dismay with Washington, only one House incumbent lost in California in the last decade.

That's changing.

A slew of hot congressional races unlike anything in recent memory will be contested on the June 5 primary ballot, after the job of crafting district boundaries was shifted to an independent commission established by voters.

The new lines, no longer drawn by state lawmakers and party power brokers to safeguard incumbents, set off a surge of retirements that left behind open seats while leaving other lawmakers facing something they've never experienced, a serious challenge.

The scenario is further rattled by a new primary system for members of Congress and state legislators in which voters, regardless of registration, can select candidates from any party. The two candidates who receive the most votes advance to the November general election, even if they are from the same party.

Two trends are emerging amid the changes.

In a state once known as a fortress of incumbency, new faces are inevitable and there is talk of surprises. With control of the House of Representatives on the line, national Republicans have said California is among the states where they could lose the most ground, even though it remains a longshot for Democrats to gain the 25 seats they need to reclaim the majority.

House Speaker John Boehner, R-Ohio, recently alluded to vulnerability for the party in the state. One reason: GOP House candidates in competitive districts could be hurt by the top of the ticket. It's been more than two decades since a Republican — George H.W. Bush — carried California in a presidential election.

Even so, national Democrats and Republicans are raising money furiously to contest individual seats in the state, including through political committees that can accept unlimited donations.

For the 53 House races, the new order in California is perhaps best showcased in Los Angeles' San Fernando Valley area, where two long-serving Democrats have been forced into a fight for a newly drawn district.

The candidates for the 30th Congressional District, Reps. Brad Sherman and Howard Berman, share liberal pedigrees and similar-sounding names. With several Republicans on the ballot dividing the GOP vote, it's possible the primary in the heavily Democratic district will be a warm-up for Sherman and Berman in a November showdown. If so, Republicans would become the key swing vote in the general election.

"How much money do we spend now, and how much do we hold? It's a hard calculus," said Sherman consultant Parke Skelton.

Berman, first elected in 1982, was chairman of the Foreign Affairs Committee from 2008 to 2010 and has locked up most of the establishment support, including from Gov. Jerry Brown and the state's U.S. senators.

Sherman, first elected in 1996, now represents about 55 percent of the new district and has been highlighting his support from former President Bill Clinton. Sherman had more than $4 million in the bank, according to fundraising totals for the first quarter of the year, compared to $2.5 million for Berman, who has been raising and spending money at a faster clip during that period.

The reshaped district lines are just part of what will make 2012 an unpredictable election season. Voters are angry over the economy and double-digit unemployment in the state, and are dismayed with lawmakers in Washington and Sacramento. A Field Poll in March found 83 percent of California voters disapprove of the job Congress is doing.

Allan Hoffenblum, publisher of the California Target Book, which provides detailed analyses of legislative and congressional races, predicts that as many as eight districts could see pairings of candidates in November from the same party.

"Some of these old bulls are going to find themselves ... going against an alternative in their own party," he said.

Overall, those same-party showdowns are likely to underscore a familiar trend in the state — that Republicans have been growing scarce. Democrats hold a 2.2-million voter edge in California, and Republicans are in danger of slipping below 30 percent of total statewide registration.

Even more telling: As of April 6, independents outnumbered Republicans in 14 of the state's 53 congressional districts, state records show.