A lack of vetting wasn't the problem.
A lack of toughness then on the part of the rest of the Republican field, who one assumes either didn't think the Howard Stern stuff was damaging (it really isn't) or didn't want to get any dirt on their shiny wing-tip shoes.
Either way if Trump was a bad as some are now trying to portray him, it would be incumbent on his primary opponents to draw attention to it.
Blaming his own supporters now for not digging up dirt on Trump is ridiculous.