In less than two months of fundraising, Kentucky Secretary of State Trey Grayson (R) raked in $602,699 for his Senate exploratory committee, and he had $571,103 in cash on hand at the end of June.Grayson, who formed his exploratory committee in early June with the blessing of Sen. Jim Bunning (R-Ky.), has said he does not plan to challenge the incumbent Senator in 2010 and will only run if Bunning decides to step aside.Bunning has not released his second-quarter fundraising report, but his lackluster performance in the last quarter of 2008 and first quarter of 2009 were two big reasons why many political insiders view him as the most vulnerable Senate incumbent this cycle. Between Jan. 1 and March 31, Bunning raised just $263,000.Bunning has left open the possibility of stepping out of the race if his fundraising continues to go badly. But privately, many state and national GOP insiders are hoping Grayson will challenge Bunning in a primary if the irascible Senator goes ahead with his re-election bid this cycle.Meanwhile, Rand Paul (R), an eye surgeon and son of Rep. Ron Paul (R-Texas), who runs a statewide taxpayers group, has also formed an exploratory committee, and he announced last week that he raised more than $100,000 as of June 30.