washington/san francisco democratic u.s. presidential candidate hillary clinton campaign solicit advice california regulators revamp federal regulation require biofuels like corn-based ethanol blend nation gasoline supply accord campaign state officials move clear sign yet elect clinton would seek adjust regulation call renewable fuel standard possibly hurt chance corn-growing state like iowa face tough battle republican rival donald trump nov. election renewable fuel standard create congress 2005 mandate transportation fuel sell unite state contain minimum volume renewable fuel intend cut greenhouse gas emissions expand u.s. renewable fuel sector low reliance import oil oppose oil industry environmentalists criticize mere subsidy corn producers clinton advisers contact california air resources board carb discuss whether policy like california low carbon fuel standard market-based system rather mandate could apply national level replace augment renewable fuel standard issue carb officials say mary nichols head carb say discuss state regulations clinton advisers backer low carbon fuel standard nichols say tell clinton advisers could avoid political backlash focus carbon-reduction strategies instead expand electric vehicle sales clean emissions coal-fired electricity nichols provide detail discussions clinton campaign official ask name confirm discussions carb give detail campaign spokesman tyrone gayle say campaign seek advice diverse set stakeholders add clinton campaign support replace rfs national low-carbon fuel standard elaborate former obama administration climate energy adviser heather zichal say sideline democratic national convention philadelphia last week renewable fuel standard break clinton administration could make modifications fix mandate necessarily perfect way regulate zichal say event u.s. corn lobby hop convince clinton trump uphold regulation require double u.s. biofuels use 36 billion gallons per year 2022 congressionally mandate volume target set expire program design last indefinitely environmentalists anti-hunger activists oil sector call rule repeal change say raise food fuel cost without deliver emissions reductions intend achieve market-based system california regulation key part state effort combat climate change require 10 percent reduction carbon intensity transportation fuel 2020 leave company decide reach target california enact low carbon fuel standard 2007 target oil refiners distributors sell state market anger midwestern ethanol interest regulation count carbon dioxide footprint transport biofuels state blend effectively block many import oil company complain regulation costly clinton may express support federal renewable fuel standard opinion piece publish iowa newspaper say could improve clinton openness overhaul renewable fuel standard appear contrast trump position state-by-state battle republican presidential nomination trump say support biofuel mandate set renewable fuel standard corn ethanol industry lobbyists say talk clinton trump campaign argue favor renewable fuel standard clinton campaign study alternative u.s. ethanol mandate