Mr Trump took to Twitter and questioned how the Democratic presidential candidate would negotiate with countries such as China, Russia and Japan. He said: “How do you think China, Russia, Japan or others would do with him in a negotiation? We would have no country left!!!”
It comes as Mr Trump and Mr Biden both hit the campaign trail on Thursday ahead of November’s presidential election.
Mr Trump hosted a roundtable in Dallas on the economic recovery from coronavirus, while Mr Biden held a similar event in Philadelphia.
Former Vice President Mr Biden formally won the Democratic nomination on June 6.
He said on Twitter: “Folks, tonight we secured the 1,991 delegates needed to win the Democratic nomination.
“It’s hard to see how he can recover from this in a broader sense, but many of his supporters still remain faithful to a president they believe is making America great again.”
Dr Moran added: “Trump’s strategy of running on the economy has been badly damaged by the economic shocks of Covid-19.
“Though last week showed some positive statistics on a possible turnaround it is very unlikely that the recovery will be as dramatic as Trump hopes, certainly not by election day.
“What is probable, as a result, is Trump positioning himself as a law and order and anti-immigration candidate.
“We are already seeing him attempt to do this with mixed success.
“I suspect we will also see very brutal attacks on Biden, linking him to the Obama Administration that so many Trump supporters opposed.
“For Trump it is about getting out his base – he has never been a candidate or president who has sought to unite the country.”