ON APRIL 12th Hillary Clinton officially entered the race for president. This comes 576 days before the general election, and she was not the first to throw her hat in the ring. Both Ted Cruz and Rand Paul had already formally declared on the Republican side, followed by Marco Rubio on April 13th. Why do candidates announce so early?

Before the 1970s campaigns tended to be shorter. Candidates often announced only a few months before election day. Campaigns grew longer after the Democrats rewrote their party rules to give more weight to primary elections in the states rather than secretive negotiations at the nominating convention. This forced candidates to make their pitches directly to ordinary voters, which takes longer (see chart). The Republicans followed suit.