ALLENTOWN – An exuberant Kamala Harris whipped up a rapturous crowd at her first rally since effectively clinching the Democratic presidential nomination, as she launched fresh attacks on Donald Trump for trying to “take the country backward.”In a stark contrast to outgoing President Joe Biden’s often stumbling and low-energy speeches, Vice President Harris gave a punchy and enthusiastic address that was greeted with cheers at the event in the battleground state of Wisconsin.Harris (59) is injecting fresh hope into the Democratic party, following 81-year-old Biden’s stunning exit from the…