He jogged back and forth across a downtown Pittsburgh street to greet people who met him with cheers of "Run Joe Run."
He said Republicans have been "wrecking the economy for a long, long time."
"You built the middle class, that's not an exaggeration."
It wasn't always about hot dogs and bounce houses.
Something to think about when you fire up the grill this weekend.
Twenty-three states had established Labor Day holidays before Congress made it a federal commemoration.