Biden says he receives briefings warning of Russian and Chinese election interference

• "China and others are engaged as well in activities that are designed for us to lose confidence in the outcome," he added.

Why it matters: Biden is leading in state and national polls against President Trump less than four months from election day. But Russian interference helped push Trump to victory in 2016, and could be a defining factor in the final stretch of the 2020 campaign season.

• The federal government began briefing presidential campaigns and national parties on election threats from foreign adversaries in recent weeks, The Washington Post reported.