Tomorrow is Super Tuesday, the single biggest day for presidential primaries. These “preference polls” (and caucuses) have loomed large in elections for years. Prognosticators start laying odds months before the first contest in Iowa. But this system wasn’t built into the Constitution. It was developed as part of Progressive Era reforms at the turn of the last century to wrest decisions from party bosses and give voters a say in who would get on the general election ballot. And the system still isn’t carved in stone. State parties can change their rules and dates, usually to find an early, more prominent place in the lineup. NCSL has more information on state primaries here.