Democratic front runner Joe Biden on Monday appealed to a billionaire Republican donor for fundraising help in his presidential campaign. But the financier, Trump-supporting New York supermarket magnate John Catsimatidis, declined. Biden spoke to Catsimatidis, who has an estimated net worth of $3.1 billion, for about 10 minutes at a fundraiser held at the New York home of short seller Jim Chanos, according to the businessman. When Biden asked for his help, “I just smiled,” Catsimatidis said. Catsimatidis, who owns the New York supermarket chain Gristedes and ran for mayor in 2013, had praise for Biden, but he is sticking...