A holiday in the city where the original Tea Party was held. It's not much of a speculative stretch to think the most extreme current tea party members imagines the tree of liberty needs watering on tax day. Of course that being said, why target the marathon and not, say, a federal office building? But whatever. A lunatic doesn't really need an excuse for their lunacy, it's us in the aftermath who feel the need to attach some meaning to the meaningless acts of madmen.