The ever-growing Democrat field for the 2020 presidential election could lead the party to the extreme left, historian Niall Ferguson told Fox News Radio host Brian Kilmeade Thursday.

“The danger for the Democrats is that they end up nominating a left-wing candidate in 2020,” Ferguson told Kilmeade.

The Stanford University Hoover Institute senior fellow warned that the Democrats in their pursuit to stop a second term for President Trump term may push them away from a mainstream candidate like former Vice President Joseph Biden.

"And the challenge for the President I think is to withstand what is going to be a very tough year reminding himself that in the end it's in 2020 that he stands for re-election and if the Democrats carry on going, as I think they are likely to, to the left and discount the idea of I don't know Joe Biden as a candidate,” Ferguson said. “If they're drawn towards Elizabeth Warren or Kamala Harris who I think is going to be quite a strong contender, then it's by no means over for this presidency.”

As the record-breaking shutdown continues, President Trump and House Speaker Nancy Pelosi continue to battle publicly over border security and the much-debated wall.

As for the President’s recent poll numbers, “Ronald Reagan had approval numbers that were very very bad in his first term by this point,” Ferguson added.

A recent Fox News poll has the President’s approval rating at 43 percent.