The idea is, every 4 years the highest position of governance is put on a trial and the population votes if they approve or disprove the way things are done and reconsider alternatives.
Besides the 4 year period for the evaluation of the highest ranking officers, there is an ample opportunity for direct intervention through other elections and NGOs.
The burden is on the US citizens but other nations holding the US nation accountable is unrealistic. The Germans were held responsible for Hitler but they lost an open war to a greater power. The US is not facing such a power.
Whatever happens is up to the US internal politics and the culture of the US nation. The best the external powers could do is to push for events that change the US populations feelings, thus affecting the judgement of the periodic reviews.