Except it won't be regular people using lie detectors on politicians. It will be government officials and big corps using lie detectors on regular people.
Also, if/when reliable lie detection tech appears, it probably won't take long for someone to develop a counter: a means of making oneself (or another person) truly believe a given statement. Of course, the first customers of such counter tech will also be governments and big corps.
I find it implausible for your level of certainty (and/or focus on listed scenarios) to be correct.
I have just received a survey questionnaire regarding future directions in EU (European Union) research funding, and thought it would be interesting to see how LessWrong would answer the main question:
Imagine that EU funding is available for one ambitious, visionary project extending beyond 2020.