Jeb Bush's plunge into presidential waters -- few politicians "actively explore" a White House run without knowing where those explorations will lead -- ends some uncertainties about the 2016 campaign and creates others.It gives shape to the Republican campaign and, if Mr. Bush prevails and if Hillary Rodham Clinton wins the Democratic nomination, sets up an epic dynastic struggle.The Republican race now is the mirror image of the Democratic race, with one brand-name candidate and a clutch of relative unknowns maneuvering for position and attention. It has taken Ted Cruz of Texas, Marco Rubio of Florida and Rand Paul of Kentucky, all first-term senators, months of exhausting efforts to attract a fraction of the name recognition or national political appeal Jeb Bush possessed even before last week's announcement.The real importance of the Bush announcement is that it prompts a series of important conflicts. Among them:-- Insurgents vs. the establishment.