The way I imagined it working, was that Technocracy would be a revolution of the elites. That the Depression lasts long enough and gets bad enough that even the political and economic elites come to believe that a change is needed, and Technocracy seems to offer a change that allows them to retain control. So the "revolution" isn't street protests or guerilla fighting, but rather a group of the Power Elite (TM) quietly meeting with the President and explaining the new reality - in other words, a quiet coup d'etat. Howard Scott is appointed Chief of Staff, technocrats are installed in key positions throughout the government, and enabling legislation is passed. Of course, once in power, the Technocrats may prove to have their own ideas about the role of the old elites in the new order.
Another option was the Technodemocrats or the other splinter group, whose name I forget. They both split off on the grounds that Technocracy, Inc., was insufficiently democratic and, in the Technodemocrats case, too politically inactive. With the right leadership, they seem like they could have turned into something instead of dissolving into the larger field of social democratic politics.
A third option would be to have the Technocrats pursue a political strategy analogous to the Libertarians. Essentially, rather than trying to gain power directly, set up think-tanks and publishing houses and lobbying groups, and slowly build influence. In which case they probably never actually come to power as Technocrats, but over a period of decades they push US policy in their direction.