By Jarrett Renshaw JENKINTOWN, Pa. (Reuters) – Congressman Conor Lamb has a message to Pennsylvania Democrats who wonder whether he is liberal enough to represent them in the U.S. Senate: He is no Joe Manchin. Locked in a tight nominating race with the Northeastern state’s progressive lieutenant governor, John Fetterman, the moderate Lamb has drawn comparisons to Manchin, a conservative Democratic Senator from neighboring West Virginia who has routinely acted as a roadblock to Democratic priorities in Congress. Manchin endorsed Lamb for his 2020 congressional bid and has helped him raise money…