JFK Jr. is not running as a Democrat, therefore the Democrats are not required to hold a debate including him. As for presidential debates including candidates from more than the GOP and DFL, we have the Commission on Presidential Debates running the show. Who are they? “…a largely secretive tax-exempt organization, created and run by former chairmen of the two major parties, funded by a small group of unidentified major donors, and designed, it seems, to exclude nearly all third-party candidates.” This group pushed out the League of Women Voters who previously had organized the debates because the Commission wanted more softball questions for candidates and to limit who can participate.
And she can admire the effect in the side mirror!