His candidacy could have been a threat to Ms Harris in crucial swing states like Michigan, though his request to appear on the ballot there was recently denied. He is currently on the ballot in nine states and has struggled to raise money.
Chase Oliver
Getty ImagesThe Libertarian Party - the third biggest political party in the country - has nominated Chase Oliver as their presidential candidate, with Mike ter Maat as his running mate.
In doing so, they spurned Mr Trump and Mr Kennedy, both of whom spoke at the party's convention this month in a bid for its support. Mr Trump received a notably unfriendly reception and lashed out at the audience during his speech.
Mr Oliver, an openly gay sales executive who previously ran on the Libertarian ticket for US congressional races in Georgia, says voters are done with picking from "the lesser of two evils".
"I'm just about to be the age of 40. I'm living the life of a normal American," he recently told BBC Americast.
"I understand what it's like to go to the grocery store with the same amount of money but seeing less and less filling up the cart. Those are things that Donald Trump and Joe Biden are so far-removed from that they just can't communicate those values anymore."
His campaign advocates for balancing the budget, ending military support to Israel and Ukraine, closing all overseas US military bases and abolishing the death penalty.
Libertarians support small government and individual freedoms, typically pulling 1-3% of the vote from Republicans.
The party's nominee in 2020 received more votes than Mr Trump's margin of defeat in three battleground states.
Robert F Kennedy Jr
Getty ImagesA former environmental lawyer known for his anti-vaccine activism, the nephew of former President John Kennedy initially sought - and failed - to run as a Democrat.
The 70-year-old then mounted an independent challenge to what he called the "two-headed monster" of American politics. Nicole Shanahan, a California lawyer and philanthropist, became his running-mate.
His populist economic message and criticism of the two major parties initially gave him a boost in the polls, on the back of the many disaffected voters unhappy with the choice of Biden or Trump, but he narrowly missed qualifying for the first presidential debate in late June.
In August, he suspended his independent run for presidency and said the principles that led him to leave the Democratic party had now compelled him "to throw my support to President Trump".