Former President Clinton swooped into Northern California on Wednesday to raise campaign cash and rally support for Proposition 87 and a Democrat who is making an unexpectedly strong challenge to Republican Rep. Richard Pombo. Proposition 87 would raise $4 billion for research into alternative energy by taxing the oil pumped in California. Opponents, mostly oil companies, have raised more than $80 million to defeat it, while supporters have raised more than $50 million, making it the most expensive ballot fight in California history. "It looks to me that the opponents are spending $100 million dollars to swell the 'I don't...