Carl in his response to Anne Applebaum's article commented:
This isn't anything like Europe with its Algerian suburbs the police can't go into.
I don't know about the French suburbs, often mainly North African around Paris and other high density, mainly non-indigenous suburbs across Europe, but know something about those here in urban England.

The police here can go into such areas, it is whether they are effective once there in their law enforcement role and in gaining public support (usually referred to as trust & confidence in the UK). There is a big difference between responding to emergency calls alongside undertaking overt 'normal' criminal investigations and the often covert way of investigating terrorism, organised crime and drugs. The differences are not religious or party political or ethnic, but a mixture.

In my limited time with US LE in urban areas it was quite obvious in some urban areas LE had access, little overt public support and could easily be seen as an 'occupying' power. A topic SWC have discussed before.

Now back to Boston. Amidst all the media reporting and I have read only a little I have yet to see a report(s) that US LE had been alerted by the suspect's family, friends and community about their changing character. Yes that is a big issue itself, for example do families notice and want to tell others?

Maybe that is what Anne Applebaum is talking about:
Our response is going to have to be different — very different — as well.