of the Post-Keynesian school, although Krugman has been critical of some Post-Keynesian economists such as John Kenneth Galbraith – whose works The New Industrial State (1967) and Economics in Perspective (1987) Krugman has referred to as not "real economic theory" and "remarkably ill-informed" respectively. In recent academic work, he has collaborated with Gauti Eggertsson on a New Keynesian model of debt-overhang and debt-driven slumps, inspired by the writings of Irving Fisher, Hyman Minsky, and Richard Koo. Their work argues that during a debt-driven slump, the "paradox of toil", together with the paradox of flexibility, can exacerbate a liquidity trap, reducing demand and employment. Free trade Krugman's support for free trade in the 1980s–1990s provoked some ire from the anti-globalization movement. In 1987 he quipped that, "If there were an Economist's Creed, it would surely contain the affirmations 'I understand the Principle of Comparative Advantage' and 'I advocate Free Trade'." However, Krugman argues in the same article that, given the findings of New Trade Theory, "[free trade] has shifted from optimum to reasonable rule of thumb ... it can never again be asserted as the policy that economic theory tells us is always right." In the article, Krugman comes out in favor of free trade given the enormous political costs of actively engaging in strategic trade policy and because there is no clear method for a government to discover which industries will ultimately yield positive returns. He also notes that increasing returns and strategic trade theory do not disprove the underlying truth of comparative advantage. In the midst of the 2009 Great Recession, Krugman made a significant departure from his general support for free trade, entertaining the idea of a 25% tariff on Chinese imports as a retaliation for China's policy of maintaining a low value for the renminbi, which many saw as hostile currency manipulation, artificially making their exports more competitive. In 2015, Krugman noted his ambivalence about the proposed Trans-Pacific Partnership, as the agreement was not mainly about trade and, "whatever you may say about the benefits of free trade, most of those benefits have already been realized" [by existing agreements]. After the 2016 elections, and Trump's moves towards protectionism, he wrote that while protectionism can make economies less efficient and reduce long-term growth, it would not directly cause recessions. He noted that if there is a trade war, imports would decrease as much as exports, so employment should