Mr Kushner, a property developer who is both President Trump’s senior advisor and son-in-law, reportedly made the remarks after he was challenged about Mr Trump’s prolonged interrogation over whether Barack Obama was born in the US.
During Mr Obama’s 2008 presidential campaign and throughout his presidency, multiple theories emerged falsely claiming he was not a natural-born American US citizen and it was therefore unconstitutional for him to become US President. Mr Trump was among those who pushed the “birther” conspiracy theory and consistently questioned former President Obama’s birthplace of Hawaii.
The former New York Observer editor has now claimed that Mr Kushner, the former publisher of the paper, informed her that Mr Trump did not believe the “birther” lies he was peddling.
“When I was the editor of the New York Observer, Kushner and I were going back and forth about how the paper should cover him,” Elizabeth Spiers wrote in a post on Twitter.
“I told Jared that I was particularly appalled by his father-in-law’s birtherism stance, which I viewed as cynical and racist.
“He rolled his eyes and said ‘He doesn’t really believe it, Elizabeth. He just knows Republicans are stupid and they’ll buy it’”.
Ms Spiers, who served as the editor of the publication from early 2011 to late 2012, made the alleged revelation in order to prove to a right-wing blogger that Mr Trump was a “notorious liar”.
“Let's be clear he was talking about you, Doug,” she says. “Trump did not con Democrats; he conned – and is still conning – his base. So you have every right to your gullibility and I won’t try to deprive you of it, but personally, I’d rather know what the hell is going on”.
Ms Spiers, who is also the founder of Gawker, also claimed that a friend of the mogul-turned-politico once told her Mr Trump would “lie to you about what time of day it is, just for the practice”.
But she is not the only person to argue that President Trump is a liar. It has been asserted by a number of politicians and commentators, with Vermont Senator Bernie Sanders branding Mr Trump a “pathological liar”.
“What do you do when you have a President-elect, soon to be President, who – and I say this not happily but I think most people who observe him would agree – is a pathological liar who changes his mind every single day?” the Democrat, who challenged Hillary Clinton for the Democratic presidential nomination, said at the end of last year.
Comedian John Oliver has also called the President a “pathological liar”. What’s more, at the beginning of the month, Quinnipiac University asked Americans for the first word which springs to mind when they think of President Trump. The answer given more times than any other was “idiot,” followed by “incompetent” and then “liar.”