Rep. Marsha Blackburn is meeting resistance from wealthy Republican donors in Tennessee, an establishment-oriented crowd more comfortable with former Gov. Phil Bredesen, the conservative firebrand’s Democratic opponent in the state’s competitive, closely watched Senate race. Republican financiers, titans of industry in Tennessee, are still gloomy about the retirement of Sen. Bob Corker, a conservative pragmatist. Many are sitting on their wallets as the crucial, 100-day mark to the midterm elections approaches. After a lifetime raising millions of dollars for GOP causes and candidates, some are even donating to Bredesen, whom they view as a centrist who will buck Senate Minority...