<p>MARSHALLTOWN, Iowa - The Southern accent had a familiar ring. So did the youthful energy, and the polite, mama's-boy manners that shined through as he locked onto voters' eyes and answered their questions by starting with, ''Yes, sir'' or ''Yes, ma'am.'' And could it be? Could this tanned, trim Democrat running for president, with floppy hair and dimples, actually be more charming than the Arkansan who sought the White House 12 years ago?</p>