There is some evidence to suggest the debate calendar does influence the actions of the candidates. Candidates who wished to participate in the May 5th debate were required to at least form presidential exploratory committees, and several of them took this step during April. Gingrich chose to announce his campaign shortly after the debate so that he would not be expected to participate in it. Several other candidates made yes-or-no decisions in the following days.
It's probable that the candidates with exploratory committees (Romney and Santorum) will make their official declarations in advance of the June 13th debate, although it's not required. Unlike the May 5th debate, it's expected that the "first tier" candidates will actually participate on June 13th.
If so, the June 13th debate will be the first real contest. The pressure will be on for the fence-sitters (people who have not ruled out a run but haven't made an exploratory committee) to join the race. Palin, Bachmann, and Huntsman should make up their minds within the month. If Palin does not intend to run, there is no particular timetable she needs to follow. Bachmann would like to ensure Palin is not running before she gets into the race herself. If no answer is forthcoming from Palin in the next few weeks, Bachmann may jump in anyway so she can participate in the debate.
Whether or not the June 13th debate will be a "real" debate would have been up to Romney, whose decision to opt out of the May 5th debate muted the event's importance. Romney may not actually be the most likely candidate to win the nomination, but he was perceived as the frontrunner. With Pawlenty's position enhanced by Daniels' departure, the pressure is on Romney. If he chooses not to participate this time, observers will be puzzled.
