You read and decide. Another interpretation is that he's merely calling for a violent revolution against the U.S. government, but not specifically for the President's blood to be spilled. Either way, it's amazingly lunatic.
UPDATE (1/14): Professor Rowley has now edited his post, removing the concluding comment about the need to water the tree of liberty with the blood of tyrants (i.e., Obama) etc. Wise move on his part. (You can see the original quote here.)