This was standard Alinsky #13 tactics.
identify, isolate, freeze and escalate
It was all carefully orchestrated and carefully marketed. Ernst was identified. He was isolated by turning him into a pariah in his neighborhood, and then the pressure only increased.
It didn't merely work because the pressure of having a mob outside your house will break anyone at some point. The neighbors will be petrified. You will become a pariah in the neighborhood, and you won't every be left alone until you give in. It worked because ACORN carefully created the mob to be most effective. Prominent among protesters were those in wheel chairs, older folks, and anyone else that portrayed the image of someone weak and helpless.
This was no accident. Alinsky works when the image is that of those with no power, no money, and no influence getting together, organizing, and creating power by getting in your face. The poor and powerless have no other outlets. So, when they go to extreme tactics it's viewed as their only outlet to affect change. So, in order for Alinsky to work, it must be viewed as being employed by the poor and powerless.
Of course, that isn't the case when President Obama uses it and certainly when they are used against Sarah Palin. Palin has been the target of the most intense Alinsky like tactics. The media mocked her for months. They also continued to increase their attacks as her star rose. Obama often mocks his opponents. He's mocked Rush Limbaugh, Fox News, Rick Santelli, and Jim Cramer. All of this is standard Alinsky isolation tactics. Obama learned all of this as a community organizer when he first became a professional. At the time, he represented those with no represeentation. At the time, these sort of tactics made sense.
Now, he is the most powerful person in the world. It's one thing for a poor lady in a wheel chair to engage in mob in your face tactics. That's extremely effective. It's quite another when the most powerful person in the world engages in mocking in your face tactics. That just lowers and cheapens the office. Furthermore, when the media as a whole engages in mocking against one individual, that only creates sympathy for the target. Alinsky's tactics can be effective in the right environment, but they won't when the president and the media uses them.