The hilarious thing about people complaining that Platner was insufficiently vetted is that he ran in the state of Maine with
zero support from the Democratic Party. The Democratic Party vets their milquetoast, genocide-loving, war supporting, affordable health-care opposing, Orange Man Bad candidates that they install as the preferred candidate. There was no such process for Platner because the Democrats never wanted him to run in the first place. Instead, they cast a wide net to look for as much stuff as they can to smear him and get him out of the race because he supports policies people actually want and opposes all the policies that the Democrats want, but sometimes pretend they support.
It would have been far easier for the Democrats to just vet their own preferred candidate that has a popular platform, but instead they ran another near-octogenarian that had no popular policies and excited nearly nobody.
Anybody can register to run for an office and be on the ballot if they have enough signatures. There is no vetting requirement and political parties are only invested in their preferred candidate. The rest are on their own.
If you have a problem with Platner getting past the primary process, take it up with the party that didn't give a compelling alternative to Platner.
Meanwhile, here is a great article by Ken Klippenstein telling you that unlike all the other lame liberal media members, there will be no apology forthcoming from him.