PHILADELPHIA — Since entering the Democratic Senate primary in Pennsylvania, Lt. Gov. John Fetterman has consistently enjoyed a huge leg up in fund-raising. He’s already known for his online small-dollar money machine, a Pennsylvania-size version of the repeat donor model pioneered by the likes of Bernie Sanders. But he’s also getting money through good old-fashioned snail mail. New financial filings last week showed that Fetterman’s campaign received about $2.1 million in unitemized, direct donations that weren’t made online. Direct donations under $200 are unitemized, meaning that campaigns …