86% chance. This replicates https://predictionbook.com/predictions/177857 . Currently, the number of officeholders not affiliated to either the Democratic or Republican parties is less than: - 17 US Representatives, out of 435 - 4 US Senators, out of 100 - 2 State governors, out of 50 Furthermore, fewer than 4 state legislative chambers have a majority of their members not affiliated to either of these parties. Nebraska's unicameral legislature doesn't count due to being non-partisan, so there are 98 state chambers. This question resolves as YES if all of these percentages (third party US Reps, Senators, Governors and state legislative chamber majorities) remain strictly below 4% until 2037-12-31. If any of these percentages go to 4% or more at any point in time, this resolves as NO at that time. The resolution criterion is percentage and not absolute number because the totals might change if, for example, a new State is admitted to the Union. What matters for resolution is the current party affiliation of officeholders, not at the time of election. Vacant seats do not count, either for the duopoly or against it - if one out of 100 Senate seats is vacant, the calculation is done over the 99 sitting Senators. In case of secession or similar shenanigans, what matters is whatever country is the clear successor of the present USA, and the market resolves as ambiguous if that becomes impossible to ascertain.