I've been playing with thoughts of the following sort. It can be vague whether something—say, a pain, an itch or a blueberry bush—is still in existence. If presentism is true, then cases where it's vague whether something is still in existence are cases where it's vague whether something exists. Thus it's somewhat harder for the presentist to avoid vagueness about existence than for the non-presentist. If one thinks that there is no vagueness about existence, this will be a problem for presentism.