See, here's the thing- you're not asking how many on the left are making those claims now. The fairer apples-to-apples question would be "how many on the Left are currently doing something similar to what Trump is doing? And I suspect you're not asking that because you know the answer is "nobody."
The big problem IMO with what Trump is doing on this voter fraud stuff is that he's not attacking a specific incident or behavior or alleged tamperer, because the election hasn't happened yet. Instead he's undermining the legitimacy of the entire process. It could easily result in voter intimidation and racial tension (he's already basically calling for it by asking his supporters to watch the polls in Philly, St. Louis and Chicago- two of those cities aren't even in swing states but see if you can figure out what they do have in common) and violent responses to the results if they don't go his way. That is a wholly different animal than, say, alleging that Katherine Harris should not have halted the recount efforts in Florida in 2000. Or, if there is evidence of tampering from Russians/hackers after November 8 2016, complaining about such tampering.
