The present paper tries to analyze, compare, and contrast the grand strategy governing the foreign policy of Bush, Obama and Trump in the time span between 2000 and 2020. Our main hypothesis is that the grand strategies of all the three US presidents fall within the category of realism. The research method is library research in that a large volume of first-hand English and also Persian sources were collected and read concerning the question of the article. With this in mind, we considered realism as the main framework for research. Bush's foreign policy grand strategy seems to be realistic, along with traces of coercive diplomacy, pre-emptive war, and war against terrorism. Then, Obama's foreign policy strategy is apparently the continuation of Bush's main foreign policy line, i. e., realism, but in the case of Obama, along with traces of internationalism, interaction and multilateralism. Finally, Trump's foreign policy grand strategy is the continuation of that of Obama, but in Trump's case, it is accompanied by traces of neo-isolationism and unilateralism. To explain the differences in the grand strategies of these three presidents and present a conceptual model, we borrowed some lessons from cognitive science achievements, especially Eleanor Rosch's theory of “ prototype" and Wittgenstein's theory of family resemblance, giving rise to the new conceptualization of category and categorization. We have considered the category of realism as a set of features that the grand strategy of Bush, Obama, Trump, or any other realist president, does not necessarily have to have all these features, and only these features. Rather, its outcome falls into this category. The result is an interdisciplinary model for determining the strategy of each of these three presidents in foreign policy, which is presented for the first time in this study, namely the model of the grand strategy of based on the theory of family resemblance and prototype.