EXCLUSIVE: Former President Trump said President Biden is a "true threat to democracy," while reacting to his opponent’s campaign speech marking three years since the Jan. 6 Capitol riot.

Biden delivered a campaign speech in Blue Bell, Pa. Friday, and spent the majority of the address attacking Trump, who holds a massive lead over the GOP presidential primary field.

Biden accused Trump of "trying to steal history the same way he tried to steal the election," while saying that the results of the 2020 election proved that he was a "loser." 

But in an interview with Fox News Digital after Biden's speech, Trump fired back.

"The Democrats rigged the last election and they are trying it again," Trump said. "But it won’t work because they have shown how bad and incompetent they are."

"Joe Biden is the worst president in the history of the United States — he is incompetent, he is crooked, and in many respects, he is Benedict Arnold," Trump told Fox News Digital. "He is destroying our country like no one else has done before." 

Trump, pointing to the crisis at the Southern Border, said the United States has "an invasion of millions of people, many from prisons, mental institutions and terrorists pouring into our country." 

"He is responsible for this," Trump said. "We are a failing nation — a nation in decline — and it is all because he is the worst president in the history of our country." 

Trump went on to tell Fox News Digital that "because of his gross incompetence, Joe Biden is a true threat to democracy."

"This is not a time for us to have a mentally challenged president," Trump said. 

Trump's comments come as Biden blasted him for "the worst dereliction of duty by a president in American history" and "an attempt to overturn a free and fair election by force and violence." 

But Trump pushed back, saying: "The only insurrection is the insurrection that is taking place at our border where he is allowing millions of people from parts unknown to invade our country at a level far worse than even a military invasion."

Trump has never been charged with insurrection, despite Special Counsel Jack Smith bringing charges against him related to an investigation into the Jan. 6 Capitol protests and the 2020 election. 

Smith charged Trump with conspiracy to defraud the United States, conspiracy to obstruct an official proceeding, obstruction of and attempt to obstruct an official proceeding and conspiracy against rights.

Trump pleaded not guilty to all charges.