In the 2012 U.S. Presidential campaign, there were a very large number of Republican primary debates. After the election was over, the Republican National Committee (RNC) concluded that that there were too many debates, and that this had a damaging effect on whoever emerges as the party nominee. So they decided that in 2016, the only Republican primary debates would be the ones sponsored by the RNC, rather than having candidates choose which debates they wanted to attend like last time, and there would be many fewer debates, about one debate per month starting this August.
My question is, how is this decision enforced? What stops a Republican candidate from attending a debate that is not sponsored by the RNC? And if nothing is stopping that from happening, are there any organizations or news outlets that are trying to host non-RNC-approved debates?