San Francisco philanthropist Susie Tompkins Buell, one of the Democratic Party's most generous benefactors, is keeping her checkbook closed when President Obama holds high-priced California fundraisers this week."I want to look him in the eye and say, 'Thank you so much' " for his work, said Buell, who expresses deep disappointment in the president's leadership on environmental issues, especially climate change. With Obama's 2012 re-election campaign in full swing, "I would just love to write my big check ... or have a high-dollar dinner here" on his behalf, she said. "I can't."Buell, a co-founder of the Esprit clothing company, has...