If I look at his body of work over the 35 years since the yearbook, then I doubt that I'll find anything evidencing racism during that span of time. So the yearbook appears to be a one-off.
But let's face it: most Democrats on this Board would want Trump to resign if he had worn blackface at age 25, some 40 years ago. There would be a total media uproar and meltdown of DEFCON 1 proportions. The rules only apply to Republicans, as Baron's post above shows.