Assuming it’s one of those Green, Libertarian, Socialist campaigns where it’s just someone running for President and no real party presence down ballot.
Let’s say they get enough votes to win. How would a third party candidate govern with a split congress made up of their party opposition? Do they cave into one side? Fight them for four years?
The veto is a strong power. And if the Congress is still staffed with do-nothings, then they can rule by executive fiat like the current administration does.