2 years
The American Experiment is built on a great many fundamental mechanisms, the interpretations of which are still being fought over, but a few are unassailable, including a two year reset.
All Congressman and Congresswomen must run for office every two years, meaning the response to a crisis can force a change in the Congress no faster, at least in a smoothly running government.
And that’s what they planned. If enough people decide that a change is needed, and can vote enough like-minded folks into office, they effectively change the government.
Democrats took effective power this term and began the work of correction. The Founders also built in a mechanism if two years is too long to wait: impeachment and the presidency was the reason.