多年来以来，学界始终保持着有关美国两党政治极化问题的热烈讨论。本文旨在解释为什么美国国会议员比普通民众更加极化，以及美国政治精英之间的两党极化将对其外交政策产生什么影响。 本文认为，国会议员之所以比普通民众更加极化，是因为通过“自上而下”与“自下而上”的两种方式，民众中更为极端的部分群体对于议员的影响力被放大了。本文以“杰利蝾螈”（不公正改划选区）为例阐述了“自上而下”机制的问题所在：有能力改变现状的群体作为既得利益者缺乏改变现状的动机。在“自下而上”的方面，本文则主要探讨了选民参与政治的积极性是如何影响立法者的政治极化的。 两党极化的加剧给美国的国内和外交政策带来了巨大的负面影响。从国内政治来说，两党极化不仅导致大量中间选民和温和派选民无法被充分代表，还会使得议员的决策以党派利益而非公共利益为先，并降低立法的效率。从外交政策来说，两党极化限制了美国可以使用的外交政策工具的类型，从而降低了美国在外交政策上的灵活性与议价能力。第二，两党极化削弱了美国制定长期、有效的外交政策的能力。第三，美国政治精英之间的党派极化损害了该国的软实力。 本文还提出了美国的两党极化对于中国的启示。首先，尽管美国政治精英在对华强硬的方面达成了一致，但在具体的对华策略上两党仍没有取得共识，这将限制美国对华实施具有一致性的长期遏制策略。其次，由于极化选民对于各个议员的影响力更大，通过影响各个议员的基础（极化）选民的意见来改变他们的政治立场更为有效，同时，也可鼓励持有对华有利立场的温和派选民更多地参与政治。第三，利用选举前的关键期向美国施压将增加中国在争端中的谈判筹码，对于“杰利蝾螈”严重的地区，党内初选比大选更为重要。最后，由于两党极化，美国的外交政策越来越缺乏一致性与可信度，因此，中国应当充分利用这一点，着眼于制定具有一致性和可信度的外交政策。
The political polarization among the U.S. political elites has been heatedly discussed for years. This thesis aims to explain the reason why U.S. Congressmen are more polarized than the general public and what impact the political polarization among the U.S. political elites will impose on its foreign policy. This thesis argues that there is a mechanism through which the influence of the more polarized groups of voters is amplified for the Congressmen. The mechanism consists of a top-down approach and a bottom-up approach. Taking the gerrymandering in the U.S. as an example, this thesis demonstrates the key point: those who are capable of making a difference have a vested interest in maintaining the status quo or even making it worse. Regarding the bottom-up approach, this thesis discusses how the activeness of voters’ participation in politics can affect the political polarization of the lawmakers.The rising political polarization brings about huge negative impact both on the domestic and foreign policy of the U.S. Domestically, it not only makes a large number of moderates and independents less represented in the current political system in the U.S., but also makes the legislation in Congress less productive. Moreover, it prompts Congressmen to make decisions driven by partisan loyalty rather than national or public interests. In terms of foreign policy, rising political polarization limits the types of foreign policy tools that the U.S. can use, leading to less flexibility and fewer bargaining chips for the U.S. in this field. Secondly, political polarization in Congress also undermines the U.S. capability to make a long-term and effective foreign policy. Thirdly, political polarization among the U.S. political elites also impairs the country’s soft power.The thesis discusses several implications for China. Firstly, while the U.S. political elites generally agree on being tough to China, there is still no bipartisan consensus on specific tactics to be tough to China. Secondly, China should try to influence the opinions of the major voter base of each lawmaker to shape their positions. Thirdly, China should also encourage moderates or independents who share a stance in favor of China to participate more in politics. Lastly, China should develop a foreign policy in sharp contrast with the U.S. foreign policy that is becoming more and more inconsistent and incredible due to political polarization.
