Bernie Sanders has scorned Donald Trump for only now declaring he believes President Obama is American-born.

While campaigning for Hillary Clinton, Vermont Senator Mr Sanders described the Republican candidate statement regarding the birther argument as "pathetic" and goes to the "root of what Trump's campaign is about".

Mr Trump led a campaign in 2011 calling for Mr Obama to release his birth certificate to show whether he was born in Kenya or Hawaii as the President stated.

The controversial businessman now claims it was his Democratic rival Hillary Clinton who first raised concerns about Mr Obama's nationality in 2008.

Mr Sanders, a US Senator for Vermont, said on CNN: "Well, isn't that something. My word, after eight years of having President Obama as president, Donald Trump now thinks he's a legitimate president.

"Well, I'm just overwhelmed with emotion. Look, this is pathetic. This goes to the root of what Trump's campaign is about.

"Let's be clear. It's about bigotry. You remember, let's all remember that a few years ago Donald Trump was the leader of the so-called birther movement."

Bernie Sanders stated Trump tried to delegitimise President Obama with the birther argument, "not disagree with him".

Donald Trump's most controversial campaign moments

He said: "This is a democracy. We can criticize Obama. It was delegitimising the first African American president in the history of our country. And the reason for that was clear.

"There are racists in this country who could never accept the fact that we had a black president. And that's what Trump was trying to do, delegitimise the president, not disagree with him.

"So I think this is part of his entire campaign of bigotry. It's against Muslims."