The president is the highest office in the gift with' people. The vice-president is the next' highest an' th' lowest. It isn't a crime exactly. Ye can't be sent to jail for it, but it's a kind iv a disgrace. It's like writing' anonymous letters.
—Peter Finley Dunne, American humorist writing in 1904 as his character Mike Dooley
The vice presidency has always been an awkward role. From the first vice president, John Adams, complaining it was, "the most insignificant office ever the invention of man contrived or his imagination conceived" to the hapless Selina Meyer in VEEP, our nation's second office has always seemed to belittle its occupant.
Even sitting vice presidents following popular presidents have found it difficult to be elected in their own right—ask Al Gore (2000) or Richard Nixon (1960).
After eight years, the public is ready for someone new, and the VP is seen as a lesser version of their president. They can try to distance themselves (as Gore did) but after years of close association with the president, the public is unpersuaded.
A vice president running in the wake of an unpopular one-term president has it even harder—ask Hubert Humphrey (1968.) If the president chooses not to run again, things are pretty bad. Humphrey's numbers improved a bit when he distanced himself from Lyndon Johnson and the unpopular Vietnam War, but not enough and too late.
This brings us to Vice President Kamala Harris.