[dragonwriter]

Actually, the Democrats aren't the only ones that have something to protect against that: while the Democrats have superdelegates to tip the scale in favor of insiders (though, as yet, the supers have never actually, AFAIK, tipped the result in a different direction than the majority of pledged delegates), they, unlike the Republicans, actually assign pledged delegates in a basically proportionate manner (there are state by state differences, but all of them are fundamentally around a proportionate baseline.)

The Republicans also have a system to prevent a popular outsider from winning, its just a different system. Rather than assigning pledged delegates in a basically proportional manner and then establishing superdelegates as a safety valve, they have designed a system to favor candidates with establishment support by, in most primaries/caucuses, giving vastly disproportionate delegates to the plurality or majority winner (in some cases, winner-take-all), a system designed to favor candidates who start off ahead, which is assumed to be (and usually is) those with the most party pedigree and establishment advance support preparing the ground.

This backfired on the establishment in this election largely because the establishment started out backing a candidate that was so unappealing to their own key supporters that even major donors were bad mouthing him from the beginning of the primary campaign and talking about how they were only giving to him because they felt compelled out of loyalty to the Party and the candidates family, which gave plenty of opportunity for a celebrity candidate to leverage free media to a powerful lead while the establishment was scrambling to adjust, which they never managed to do.