By Rick HowlettA new Courier-Journal/WHAS11 Bluegrass Pollfinds Bowling Green opthalmologist Rand Paul maintaining a double-digit lead over Secretary of State Trey Grayson in the Republican primary for Kentucky's U.S. Senate seat.In the Democratic race, the poll has Lt. Governor Daniel Mongiardo with a one point lead over Attorney General Jack Conway. The Democratic poll has a margin of error of 3.9 percentage points. Mongiardo led Conway by three points in an April poll and was ahead by 18 points in a March survey.The poll, conducted by SurveyUSA, give Paul a 16 percentage point lead over Grayson. Paul led in an April poll by 15 percent. The GOP poll has a margin of error of 4.8 percentage points.