I don't believe the mainstream media will question the tactics or progressive agendas of the left. Most on missfires have questioned specific policy, not the vagueness of incumbency.

Similarly with the Tea Party. Seems like they question the policy of the current administration and came to prominence based on the direction of the current folks, not to question the meaning of the GOP. They seem to be aware that their presence will be shown in a negative light, yet they persevere. I believe the Tea Party fits your concept of the big tent, with the one exception of no compromise on core principals.