US President Donald Trump told a Pennsylvania crowd on Tuesday that he’s fighting “Marxists” and “lunatics” while his Democratic challenger Joe Biden accused him in Florida, another key electoral state, of having treated Americans as “expendable” during the Covid-19 pandemic.With three weeks until the November 3 election and badly down in the polls, Trump fired every lurid exaggeration about the Democrats and insult about Biden’s mental state that he has in his arsenal.He said Biden was …