"There's never a dearth of reasons to shoot at the President"

This quote by Don DeLillo suggests that there is constantly a factor to criticize the President. It indicates that no matter what the President does, there will always be somebody who disagrees with it and will want to express their opinion. This might be translated as a commentary on the present political environment, where it seems like there is constantly somebody who is willing to criticize the President and their policies. It could likewise be seen as a warning to the President that they need to constantly be prepared to face criticism and opposition. Ultimately, this quote recommends that no matter what the President does, there will always be somebody who is willing to express their viewpoint and shoot down their ideas.