MIAMI (Reuters) - President Barack Obama had a message for his political friends and foes on Monday -- "just because I'm skinny doesn't mean I'm not tough." Obama was in Miami raising $1.5 million for Democratic congressional candidates for the 2010 elections, in which Democrats are seeking to hold onto their strong majorities in the House of Representatives and the Senate. After weeks in which he has been angrily criticized by some on the right, to the point of creating a poster image of him with a Hitler mustache, Obama told a fund-raising event that some of his supporters have...