Challenger John Kerry, who according to campaign sources is expected to announce his running mate this morning, will lead President Bush by 15 points when the Democratic convention wraps up at the end of July, according to a top Bush campaign adviser. Presidential hopeful Sen. John Kerry reacts after a speech by his wife Monday at an Independence Day celebration in Fox Chapel, Penn. Gerald Herbert, Associated Press In a memo to campaign leadership Monday, Matthew Dowd, Bush's chief strategist, said Kerry is about to benefit from "the average challenger's bounce." "We should expect the race to swing wildly to...