DALLAS - When a pair of Mormon missionaries knocked at the door of Jerry Pierce's home in a north Dallas suburb last month, he marshaled his arguments and stood his ground. "I look forward to encounters like that. I like to talk to them about the nature of Christ and who Jesus is," said Pierce, a staunch Southern Baptist, the biggest Protestant denomination in the United States. Mitt Romney, a Mormon, is running into similar resistance as he tries to win over Southern Baptists and other evangelical Protestants in the race for the Republican Party's nomination for the 2008 U.S....