(CNN) Democratic presidential nominee Joe Biden said Monday that the United States is facing one of the most difficult moments in the nation's history, with "four historic crises all at the same time." "The worst pandemic in a hundred years, that's already killed nearly 200,000 people and counting. The worst economic crisis since the Great Depression, that's cost tens of millions of American jobs and counting. And undeniable acceleration of the punishing reality of climate change on our planet, on our people, on the lives and livelihoods," Biden said in Wilmington, Delaware.