Experts say Vice President Kamala Harris and President Joe Biden’s joint Labor Day appearance in Pittsburgh shows a recognition that Democrats need to do more in so-called “Blue Wall” states — and cemented a “passing of the torch.” Biden and Harris told rally-goers in the industrial city that U.S. Steel should remain in U.S.owned and operated as they opposed a deal that would merge the firm with Nippon Steel of Japan. The duo also made their case as to why labor unions ought to vote blue in November. Speaking Monday on “The Situation Room” with fill-in host Alex Marquardt, Jasmine Wright of No…