President Trump's former White House chief of staff Reince Priebus says the 2020 election will be the "biggest political battle in modern history."

"For a Republican to win Wisconsin, Michigan, and Pennsylvania at any given presidential election will be tough. It will be a fight. This will not be easy. It doesn't matter... This is going to be a fight," Priebus said Monday on "The Ingraham Angle."

TRUMP INVITES SUPPORTER WEARING WALL SUIT TO PENNSYLVANIA RALLY STAGE

"The Democrats are energized, the Republicans will be energized and this will be the biggest political battle in modern history."

Trump focused on the economy at a fiery rally Monday at the Energy Aviation Hangar in Montoursville, Pennsylvania, just two days after 2020 Democrat presidential frontrunner Joe Biden held his own campaign rally in nearby Philadelphia.

Priebus, the former Republican National Committee chairman, criticized the Democratic presidential candidates platform, in particular Joe Biden, saying it will be tough to run against Trump's economic numbers.

"You cannot win Wisconsin, Michigan and Pennsylvania on a $93 trillion green new deal, 600,000 per household, $32 trillion in a health care package. It's not going to work. So the Trump campaign, I believe, is going to jam down the throats of every person that is watching on television these numbers," Priebus said.

CLICK HERE FOR THE FOX NEWS APP

In a video posted on Saturday, Biden is seen fielding a question from a member of the Youth Climate Strike, a group which organized over 100 marches worldwide by young people to protest climate change in March.

"You know, I'm the guy that did all this stuff," Biden said. "Read RealClearPolitics, it'll tell you how I started this whole thing back in '87 on climate change."

Fox News' Gregg Re and Anna Hopkins contributed to this report.