BOSTON --Republican Mitt Romney gathered more than 350 of his strongest supporters for a glitzy fundraising blitz Monday aimed not only at financing his fledgling presidential campaign, but also scaring off potential rivals and putting existing ones on notice. The former Massachusetts governor raised more than $2.5 million in less than six hours, but he and his staff expected the daily total to smash earlier fundraising numbers for Sen. John McCain, R-Ariz., and former New York Mayor Rudy Giuliani, who also have created 2008 exploratory committees. Both raised less than $2 million in their initial fundraising ventures. "I think it's...