According to Maureen Dawd’s article titled “Field of Dashed Dream’ appearing on August 16 New York Times, President Obama took a strong verbal punch on the chin from a woman supporter at a town hall meeting at the Seed Savers Exchange in Iowa. She asked the President "what had gone wrong" with him, and continued:
“So when you ran for office you built a tremendous amount of trust with the American people, that you seemed like someone who wouldn’t move the bar on us. --- And it seems as if your negotiating tactics have sort of cut away at that trust by compromising some key principles that we believed in, like repealing the tax cut, not fighting harder for single-payer. Even Social Security and Medicare seemed on the line when we were dealing with the debt ceiling.”
I don’t understand what ‘move the bar on somebody’ mean. I checked the meaning of this phrase on the Google, but couldn’t find out any definition.