By Michelle Conlin and Grant Smith NEW YORK (Reuters) – Within minutes of Jeb Bush dropping out of the presidential race Saturday night, some of his donors were preparing to throw their financial support behind Marco Rubio, who has emerged as the strongest candidate among the establishment wing of the party. "Jeb's network is already naturally migrating to Marco," said Gaylord Hughey, a top Bush fundraiser from Texas, echoing what four other top donors told Reuters. "It's the clear path." "It's a stampede," added another donor, who spoke on the condition of anonymity because he wanted to give Bush some time after dropping out before he went public with his support of Rubio, the U.S. senator from Florida.