Contra Costa Supervisor Karen Mitchoff proved a formidable negotiator as the swing vote in last week's fractious 3-2 approval of the board's new political district boundaries.

She refused to give up a single block of Concord to another district despite fierce behind-the-scenes lobbying and sniping about her recalcitrance.

Both maps on the table last week would have given Mitchoff what she wanted.

So, why did she reject the largely status quo map offered by colleagues Mary Nejedly Piepho and Gayle Uilkema and support the big-change option from fellow supervisors Federal Glover and John Gioia?

Uilkema and Piepho's map, after all, split no cities and left the current lines largely intact.

"Person after person told us, 'Don't split my city!' and they were ignored," Piepho said. "There were alternatives that would not have split any cities. Instead, we are splitting Pinole, Antioch, Walnut Creek, the San Ramon Valley and Morgan Territory from Clayton. We should have tried to find a map that would have gotten five votes."

Mitchoff says she was persuaded by arguments that adopting a variation of the existing lines would perpetuate the mistake of 2001, when supervisors drew East Contra into a San Ramon Valley district as a means to weaken the political aspirations of then-Supervisor Donna Gerber.

"Lots of people told us it was a bad map that needed (to be) corrected," Mitchoff said. "I agree. But at the same time, I had to fight for my district and I would venture to say that my colleagues would have done the same thing if they had been in my position."

Mitchoff's verdict means half the county's residents will have a new county supervisor as early as the fall.

Whether or not the average resident will even notice is a debate for another day.

But the political movers and shakers in the county recognize the implications.

They say the shift will help the vulnerable Democratic Glover win re-election and hurt the chances of Republicans Uilkema and Piepho. All three are up for re-election in 2012.

Yes, yes, these are nonpartisan seats, but parties view local offices as a part of their bench, and several prominent local Democratic Party leaders were highly visible at the map hearings.

Glover keeps Pittsburg and Bay Point but shifts west into substantially bluer territory -- Clyde, Martinez, Crocket, Rodeo, Hercules and portions of Pinole. He loses Antioch, where he has suffered bad publicity centered on county oversight of housing vouchers.

While Glover may benefit under voters who don't know him, others bet that Uilkema will lack the incumbency advantage in the new San Ramon Valley portion of her revised district.

The most talked-about potential challenger is Tomi Van de Brooke, a Contra Costa Community College Trustee from Orinda and Piepho's former chief of staff.

Other candidates could emerge, too. Uilkema hasn't had a real challenger in years, and some view her as beatable.

Piepho is in the strongest re-election position. She is a strong campaigner who has survived two hard-fought elections, the first against an incumbent and the second, a termed-out state assemblyman.

She could have opponents, though. Oakley Mayor Jim Frazier, Antioch Councilman Gary Agopian, Antioch Mayor Jim Davis and Brentwood Mayor Bob Taylor have all been mentioned.

But as we know, there's a gap -- read "dollars" here -- between talking about running for office and actually running for office.

SPEAKING OF OFFICES: With the new districts expected to go into effect in the fall, some supervisors will have to move.

Uilkema's Martinez office will no longer be in her district and Piepho won't need her Danville digs.

Glover says he will likely downsize his Pittsburg office, relocate to Martinez and open a satellite in Hercules.

"I'm looking for rent-free space," Glover said.

Aren't we all?

COINCIDENCES: Mitchoff assured the audience during last Tuesday's hearing that none of the four supervisors (Piepho didn't go) who attended the National Association of Counties Conference in Portland the previous week used the time to sway the map vote.

"There were no violations of the Brown Act," Mitchoff said, referring to the law that requires electeds to conduct business in noticed public meetings rather than Portland hotels.

Mitchoff and Uilkema did shop together -- they are both very stylish dressers -- but one hopes they had better things to talk about as they perused the shoe section than maps.

GOT POLITICS? Read the Political Blotter at IBABuzz.com/politics.

AND FINALLY: If Contra Costa supervisors had failed to adopt new districts by Nov. 1, the job would have gone to an unlikely trio: Assessor Gus Kramer, District Attorney Mark Peterson and Clerk-Recorder Steve Weir.

The charmingly cantankerous Kramer had a map ready to go: Concentric circles that resembled a bull's eye target.

It just goes to show that in government, things can always be worse, much worse.

Contact Lisa Vorderbrueggen at 925-945-4773, lvorderbrueggen@bayareanewsgroup.com, IBABuzz.com/politics or Twitter.com/lvorderbrueggen.