Presidential historian Douglas Brinkley looks at the considerable, often heroic achievements of Joe Biden, and at the mistakes that may color historians' view of his presidency, as the man Biden warned is a threat to democracy re-enters the White House.

Historians say it will take years to fully assess Joe Biden's legacy, but several spoke to ABC News to offer a glimpse of their view on his presidency.

As the Biden administration draws to a close, the assessments have begun to roll in. There have been looks back to the pandemic, the withdrawal from Afghanistan, the response to wars in Ukraine and the Middle East,