No. of Recommendations: 1
Here, let's quote from the article again.
Anticipate the influence of advisers. Top leaders often take a “big picture” approach and let their close advisers negotiate the details. For this reason, it’s often wise to negotiate with those advisers directly. Lobby them for support, and encourage them to get leaders on board. If advisers won’t fall in line, look for ways to reduce their influence on the leader.
Establish a representative working group. The Gang of 6’s deal was thwarted by hard-line voices on immigration that felt excluded from the negotiations. When appointing a committee to represent a larger group, make sure it includes the full range of perspectives.
You fell into the trap of assuming that just because the Gang of 6 represented what the dems want that the GOP members could say the same about their side. In this case, they couldn't, and the deal died.