The poll comes just ahead of the vice presidential debate in Danville, Ky., on Thursday.

Biden's unfavorables are higher than they were in September 2008, before he squared off against Sarah Palin in the vice presidential debate. Ahead of that debate, Biden was viewed favorably by 53 percent of registered voters while 31 percent had an unfavorable view of the then-Democratic senator from Delaware, according to Pew Research. Pew found in 2008 that 51 percent of registered voters viewed Palin favorably and 40 percent viewed her unfavorably.

The most recent Pew survey was conducted from Oct. 4-7 among 1,511 adults and 1,201 registered voters. The margin of error for registered voters was plus or minus 3.3 percentage points.