Theos was speaking after the Republican presidential candidate squared off against Hillary Clinton in the first of three TV debates last night.
The hour-and-a-half spectacle saw the two White House candidates discuss a wide range of topics from unemployment, economy, taxation and national debt to terrorism, immigration, Islamic State and nuclear weapons.
It's thought 100 million people tuned in live to watch the debate.
Hillary Clinton's lead over Donald Trump in the polls has decreased in recent weeks, with a recent RCP survey putting the Democrat at 47 per cent and the Republican at 45 per cent. Her lead previously had been in double figures.
However most polling on the debate showed Hillary Clinton to be the winner.
She accused Donald Trump of sexism and racism, and said he had "something to hide" because he hadn't published his tax return.
Donald Trump claimed Hillary Clinton did not have the "stamina" to be US president, and also said state secrets were not safe with her after she used her private email account to send messages while she was Secretary of State.
Speaking on Premier's News Hour Paul Bickley, from Theos, said: "What struck me was Trump's lack of detail, and I think this will come through now.
"In the Republican primary debate it was much more freewheeling. Now, people are facing the prospect of who they are going to appoint as their commander-in-chief.
"They will want to know that that person will be able to master the detail and Clinton was particularly good at that in comparison to Trump... I think he's going to have to be better on the detail."
Listen to Premier's Hannah Tooley speaking to Paul Bickley on the News Hour:
