This is tracked by Our World In Data's Democracy Data Explorer which uses data from The Varieties of Democracy (V-Dem) project and currently lists the US central estimate at 0.82. 0.80 is the lowest central estimate for the US since 1975.
If Trump does not win the 2024 general election, this will resolve NA. Otherwise:
If the 2025 central estimate for the US falls to 0.79 or below, this resolves YES
Otherwise, resolves NO

Partner market: /probajoelistic/-if-trump-loses-will-the-us-elector
Update 2026-03-02 (PST) (AI summary of creator comment): The market will resolve when the V-Dem data is updated with 2025 data, which is expected in March 2026.
I was curious when this will likely resolve, and found this in the "Learn more about this data" popup in the linked explorer: "Next expected update: March 2026". Presumably that will be the update that adds the 2025 data point.