US President Donald Trump has warned his Democratic challenger Joe Biden will "demolish" the American dream if he wins the White House in November. Speaking on the final night of the Republican convention, the president depicted his opponent as "the destroyer of American greatness". Trump 2020 campaign advisor Mica Mosbacher told Justin Webb: "This was perhaps the most consequential speech of his presidency...and I think his tone was perfect pitch." She went on to say: "What I think is going on in this country is that we have two warring ideologies, two different visions. The America as we know it under the GOP, our traditional GOP values, standing for the flag and for capitalism - verses a radical, left wing, socialistic agenda which would, as Trump said, completely undermine America as we know it today." With BBC North America Editor Jon Sopel and BBC New York correspondent, Nick Bryant.