Top Democrats came to Joe Biden’s defense on Sunday, emphasizing the president’s viability for re-election amid his colleagues’ worries that voters see him as too old – concerns compounded by Donald Trump’s lead over him in recent polls.On ABC This Week, host George Stephanopoulos pointedly asked Biden’s transportation secretary Pete Buttigieg: “How can an 81-year-old incumbent be the candidate of change? It’s so critical in presidential elections.”Buttigieg replied that Biden’s administration had focused on “issues that matter most to newer generations”, including…