Tough questions yes, but not BS gotcha questions about things that aren't important.
Format:
1) Neutral moderators who stay in the background
2) Rather than narrow, often meaningless and stupid questions, that are given to only certain candidates (what a stupid format - can’t compare that way with the “moderators” picking for their own purposes who answers which issue), instead revolve the discussion around four or five generally-agreed top issues of the day: a) big government b) the economy c) illegal immigration d) foreign policy e) national security
3) An open discussion of each issue, one issue at a time for a certain time period. Maybe each with brief opening statements on the issue, then opening it up to any and all to participate. This would of course also allow for meaningful open discussion and debate allowing the audience to actually compare and contrast the candidates, instead of these stupid 30-second sound bytes.
You may have to have some sessions that will mirror the 2016 General Election debate format to see how Republican candidates would do against Hillary or whoever the Socialist Democratic Party candidate is.