It began with a hashtag — #fitn. On the eve of January’s Republican presidential primary, it seemed that every member of the political press, election observer, and New Hampshirite had adopted #fitn as a sort of quasi-official tag. It was a reference to “First in the Nation,” a long-used political phrase that dates back to the 1920s. As I watched those tweets fly by, it struck me how ubiquitous its shorthand version had become online. Where did the hashtag come from? Who first injected it into the tweet stream? Twitter’s internal search engine, as it turns out, only goes back so far. I fired up Topsy.com, by general consensus the best tweet search tool going today. But I hit the outer limits of Topsy’s archive far before I uncovered my proto-tweet. I asked Twitter HQ. No go. A smallish company, it lacks the resources, they said, to track a hashtag back to its starting point.