The democratic presidential candidates will share a stage in Johnston on Sunday in a televised debate. Just 16 days remain before Iowa’s lead-off Caucuses indicate which candidates have caught fire, and which have burned out. Four of the contestants — former Governor Howard Dean, Missouri Congressman Richard Gephardt, Massachusetts Senator John Kerry and North Carolina Senator John Edwards — are dedicating much of their campaign time to Iowa this month. An interesting test of candidate pulling power will be seen in Boone today, as Dean and Kerry both plan to appear at separate events there. The debate on Sunday begins at two o’clock on Iowa Public Television and will be simulcast by some Radio Iowa stations. With Howard Dean a narrow front-runner in Iowa, expect some of the other candidates to focus their verbal venom on him. Gephardt has repeatedly hammered at Dean since this fall, and renewed his attacks yesterday. Gephardt said Dean can dish it out, but can’t take it when his democratic rivals attack, and Gephardt warned Dean would “lose his cool” in a match-up against President Bush.