Donald Trump and his Democratic rival Joe Biden traded tough blows Monday as the White House race entered its final stretch, with the Republican leader branding his opponent “stupid” – and the Democrat firing back that the president lacked the “guts” to tackle the Covid-19 pandemic.As Biden and his running mate Kamala Harris took their campaign message to must-win swing states Pennsylvania and Wisconsin, the president convened a surprise news conference at the White House.In a freewheeling and…