Why did Justice Department officials attended at least a dozen political briefings at the White House since?

nothing at this point, you apparently didnt read the entire article. the meetings were held at the white house not the justice dept. and the content at this point does not appear to violate any other DOJ regulations. They may well have been discussing voting irregularities surrounding the election which would fall under the pervue of the DOJ. Something more might come of this, but I doubt it. The washington post has a history of grabbing the wrong end of the stick and beating the bushes with it.