In this part of the lecture I have argued that a number of works in development economics written during the 1950s contained, more or less explicitly… - Paul Krugman

From the point of view of a modern economist, the most striking feature of the works of high is their adherence to a discursive, nonmathematical style. Economics has, of course, become vastly more mathematical over time. Nonetheless, development economics was archaic in style even for its own time. Of the four most famous high development works, Rosenstein-Rodan's was approximately contemporary with Samuelson's formulation of the Heckscher–Ohlin model, while Lewis, Myrdal, and Hirschman were all roughly contemporary with Solow's initial statement of growth theory.
This lack of formality was not because development economists were peculiarly mathematically incapable. Hirschman made a significant contribution to the formal theory of in the 1940s, while Fleming helped create the still influential of s. Moreover, the development field itself was at the same time generating mathematical planning models—first Harrod–Domar type growth models, then linear programming approaches that were actually quite technically advanced for their time.
So why didn't high development theory get expressed in formal models? Almost certainly for one basic reason: the difficulty of reconciling economies of scale with a competitive market structure.

The way to deal with China would have been a broad coalition of countries that play by the rules. Instead, we've conveyed the message that big countries don't need no rules. And China is a very big country.

To be a progressive, then, means being a partisan—at least for now. The only way a progressive agenda can be enacted is if Democrats have both the presidency and a large enough majority in Congress to overcome Republican opposition. And achieving that kind of political preponderance will require leadership that makes opponents of the progressive agenda pay a political price for their obstructionism—leadership that, like FDR, welcomes the hatred of the interest groups trying to prevent us from making our society better.