Stefan Krasa and Mattias K.Polborn in this framework,gerrymandering districts affects only lican candidate as a 'supporter'of the 'Bush agenda'or candidate positions in the gerrymandered districts but as a 'rubberstamp,'Democrats believe the President's does not help a party to increase their expected rep- low approval ratings are a stone they can use to sink resentation in Congress.These predictions are cer- their opponents [...Democratic Sen.Hillary Clinton tainly empirically incorrect,but understanding why is of New York got the most mentions in Republican ads challenging. holding forth the supposed horrors of a Democratic- In our model,voters'utility depends on both their controlled Senate [...The runner-up is'San Francisco local representative's position,and the position of the Liberal Nancy Pelosi,'who is mentioned in at least 6 majority party.In the general election,voters take into GOP ads as a reason not to vote for a Democrat who account the two local candidates'positions,as well as would in turn vote to make her Speaker of the House."5 the chance that the election outcome in their district In contrast to the classical one-district spatial model, may change which party is the majority party in the the ideological composition of districts in our model legislature. does not only influence the ideological position of The latter effect implies that,in most districts,the elected candidates,but also the chances of parties to median voter cares not just about the local candidates' win,thus increasing partisan incentives for gerryman- positions when deciding whom to vote for,but also dering.Gerrymandering or,more generally,the intensi- about their party labels,as they are associated with fication of the median ideological preferences in some different national positions.The favored party's pri- districts,affects the political equilibrium even in those mary voter can exploit this situation by nominating a districts where the median voter preferences remain 元 more extreme candidate than the general election me- the same as before.Our results imply that testing for dian voter would prefer.In particular,if voters care the causal effect of gerrymandering on polarization in sufficiently strongly about national positions relative Congress is more complicated than the existing litera- to local candidate positions,then the favored party's ture has recognized. primary voter can simply nominate his own preferred 4 candidate and still win,generally even with a strict su- permajority of votes. RELATED LITERATURE The local general election loses some of its disci- Ever since Downs's(1957)seminal work,candidates' plining force because the voters'national preference position choice is a central topic in political economy factors in their vote choice.The electoral prospects While the classical median voter framework identi- of candidates in a given district are influenced by the fies reasons for platform convergence,many subse- expected ideological position of their parties'winning quent electoral competition models develop different candidates elsewhere.The association with a party that reasons for policy divergence,including policy moti- is not attuned with a district's ideological leanings may vation (Wittman 1983:Calvert 1985:Londregan and be poisonous for a candidate,even if his own policy po- Romer 1993:Osborne and Slivinski 1996:Besley and 是 sitions are tailor-made for his district. Coate 1997:Martinelli 2001:Gul and Pesendorfer Consider,for example,Lincoln Chafee,the former 2009);entry deterrence (Palfrey 1984;Callander 2005); Republican U.S.senator from Rhode Island,who had agency problems(Van Weelden 2013);incomplete in- taken a number of moderate and liberal positions that formation among voters or candidates (Castanheira 5.501g brought him in line with voters in his state.2 As the New 2003;Bernhardt,Duggan,and Squintani 2007;Callan- York Times reported,in the 2006 election,"exit polls der 2008):and differential candidate valence (Bern- gave Senator Lincoln Chafee a 62 percent approval hardt and Ingberman 1985;Groseclose 2001;Krasa and rating.But before they exited the polls,most voters re- Polborn 2010b,2012:Bierbrauer and Bover 2013). jected him,many feeling it was more important to give Most of the literature looks at isolated one-district the Democrats a chance at controlling the Senate."3 elections.Exceptions are Austen-Smith(1984);Snyder His Democratic challenger Whitehouse "succeeded (1994);Ansolabehere,Leblanc,and Snyder(2012)and by attacking the instances in which Chafee supported subsequent work by Polborn and Snyder (2017).In his party's conservative congressional leadership Austen-Smith(1984),the party that wins the majority (whose personalities and policies were very unpopular, of n districts implements an aggregate of its candidates' state-wide).'4 positions.Each district candidate chooses his position In a review of 2006 campaign ads,factcheck.org sum- to maximize his chance of winning.If an equilibrium marized:"President Bush was far and away the most exists,then both party positions fully converge to the frequent supporting actor in Democratic ads [...The median voter in the median district,even though indi- strategy is clear:whether they're referring to a Repub- vidual candidates'positions differ.In contrast,in our model,positions are chosen by policy-motivated pri- In 29.4%of U.S.Senate elections between 1922 and 2004 without an mary voters,and voters care about both national party incumbent running,the winner received a vote share that was at least positions and local candidates.In our equilibrium,na- 20 percentage points larger than the loser's vote share. tional party positions diverge,and we can analyze the 2 For example,Chafee was pro-choice,anti-death-penalty,supported effects of gerrymandering and of more or less radical gay marriage,and voted against the Irag war (see http://en.wikipedia primary voters. org/wiki/Lincoln_Chafee). 3"A GOP Breed loses its place in New England,",New York Times, November 27 2006. See http://en.wikipedia.org/wiki/Lincoln_Chafee See https://www.factcheck.org/2006/11/our-2006-awards. 810Stefan Krasa and Mattias K. Polborn in this framework, gerrymandering districts affects only candidate positions in the gerrymandered districts but does not help a party to increase their expected rep￾resentation in Congress. These predictions are cer￾tainly empirically incorrect, but understanding why is challenging. In our model, voters’ utility depends on both their local representative’s position, and the position of the majority party. In the general election, voters take into account the two local candidates’ positions, as well as the chance that the election outcome in their district may change which party is the majority party in the legislature. The latter effect implies that, in most districts, the median voter cares not just about the local candidates’ positions when deciding whom to vote for, but also about their party labels, as they are associated with different national positions. The favored party’s pri￾mary voter can exploit this situation by nominating a more extreme candidate than the general election me￾dian voter would prefer. In particular, if voters care sufficiently strongly about national positions relative to local candidate positions, then the favored party’s primary voter can simply nominate his own preferred candidate and still win, generally even with a strict su￾permajority of votes. The local general election loses some of its disci￾plining force because the voters’ national preference factors in their vote choice. The electoral prospects of candidates in a given district are influenced by the expected ideological position of their parties’ winning candidates elsewhere. The association with a party that is not attuned with a district’s ideological leanings may be poisonous for a candidate, even if his own policy po￾sitions are tailor-made for his district. Consider, for example, Lincoln Chafee, the former Republican U.S. senator from Rhode Island, who had taken a number of moderate and liberal positions that brought him in line with voters in his state.2 As the New York Times reported, in the 2006 election, “exit polls gave Senator Lincoln Chafee a 62 percent approval rating. But before they exited the polls, most voters re￾jected him, many feeling it was more important to give the Democrats a chance at controlling the Senate.”3 His Democratic challenger Whitehouse “succeeded by attacking the instances in which Chafee supported his party’s conservative congressional leadership (whose personalities and policies were very unpopular, state-wide).”4 In a review of 2006 campaign ads, factcheck.org sum￾marized: “President Bush was far and away the most frequent supporting actor in Democratic ads [...] The strategy is clear: whether they’re referring to a Repub￾In 29.4% of U.S. Senate elections between 1922 and 2004 without an incumbent running, the winner received a vote share that was at least 20 percentage points larger than the loser’s vote share. 2 For example, Chafee was pro-choice, anti-death-penalty, supported gay marriage, and voted against the Iraq war (see http://en.wikipedia. org/wiki/Lincoln_Chafee). 3 “A GOP Breed loses its place in New England,”, New York Times, November 27, 2006. 4 See http://en.wikipedia.org/wiki/Lincoln_Chafee. lican candidate as a ‘supporter’ of the ‘Bush agenda’ or as a ‘rubberstamp,’ Democrats believe the President’s low approval ratings are a stone they can use to sink their opponents [...] Democratic Sen. Hillary Clinton of New York got the most mentions in Republican ads holding forth the supposed horrors of a Democratic￾controlled Senate [...] The runner-up is ‘San Francisco Liberal Nancy Pelosi,’ who is mentioned in at least 6 GOP ads as a reason not to vote for a Democrat who would in turn vote to make her Speaker of the House.”5 In contrast to the classical one-district spatial model, the ideological composition of districts in our model does not only influence the ideological position of elected candidates, but also the chances of parties to win, thus increasing partisan incentives for gerryman￾dering.Gerrymandering or,more generally, the intensi￾fication of the median ideological preferences in some districts, affects the political equilibrium even in those districts where the median voter preferences remain the same as before. Our results imply that testing for the causal effect of gerrymandering on polarization in Congress is more complicated than the existing litera￾ture has recognized. RELATED LITERATURE Ever since Downs’s (1957) seminal work, candidates’ position choice is a central topic in political economy. While the classical median voter framework identi￾fies reasons for platform convergence, many subse￾quent electoral competition models develop different reasons for policy divergence, including policy moti￾vation (Wittman 1983; Calvert 1985; Londregan and Romer 1993; Osborne and Slivinski 1996; Besley and Coate 1997; Martinelli 2001; Gul and Pesendorfer 2009); entry deterrence (Palfrey 1984; Callander 2005); agency problems (Van Weelden 2013); incomplete in￾formation among voters or candidates (Castanheira 2003; Bernhardt, Duggan, and Squintani 2007; Callan￾der 2008); and differential candidate valence (Bern￾hardt and Ingberman 1985;Groseclose 2001;Krasa and Polborn 2010b, 2012; Bierbrauer and Boyer 2013). Most of the literature looks at isolated one-district elections. Exceptions are Austen-Smith (1984); Snyder (1994); Ansolabehere, Leblanc, and Snyder (2012) and subsequent work by Polborn and Snyder (2017). In Austen-Smith (1984), the party that wins the majority of n districts implements an aggregate of its candidates’ positions. Each district candidate chooses his position to maximize his chance of winning. If an equilibrium exists, then both party positions fully converge to the median voter in the median district, even though indi￾vidual candidates’ positions differ. In contrast, in our model, positions are chosen by policy-motivated pri￾mary voters, and voters care about both national party positions and local candidates. In our equilibrium, na￾tional party positions diverge, and we can analyze the effects of gerrymandering and of more or less radical primary voters. 5 See https://www.factcheck.org/2006/11/our-2006-awards. 810 Downloaded from https://www.cambridge.org/core. Shanghai JiaoTong University, on 26 Oct 2018 at 03:53:05, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0003055418000503