To what extent is party loyalty a liability for incumbent legislators? Past research on legislative voting and elections suggests that voters punish members who are ideologically "out of step" with their districts. In seeking to move beyond the emphasis in the literature on the effects of ideological extremity on legislative vote share, we examine how partisan loyalty can adversely affect legislators' electoral fortunes. Specifically, we estimate the effects of each legislator's party unity-the tendency of a member to vote with his or her party on salient issues that divide the two major parties-on vote margin when running for reelection. Our results suggest that party loyalty on divisive votes can indeed be a liability for incumbent House members. In fact, we find that voters are not punishing elected representatives for being too ideological; they are punishing them for being too partisan.

Bill cosponsorship has become an important part of the legislative and electoral process in the modern House of Representatives. Using interviews with congressional members and staff, I explain the role of cosponsorship as a signal to agenda setters and a form of position taking for constituents. Regression analysis confirms that cosponsoring varies with a member's electoral circumstances, institutional position, and state size, but generally members have adapted slowly to the introduction of cosponsorship to the rules and practice of the House.

What is a party? This article presents the argument that rmal party apparatus is only one part of an extended network of interest groups, media, other advocacy organizations and candidates. The authors have measured a portion of this network in the United States systematically by tracking lists of names transferred between political organizations. Two distinct and polarized networks are revealed, which correspond to a more liberal Democratic group and a more conservative Republican group. Formal party organizations, like the Democratic National Committee and the Republican National Committee, tend to receive information within their respective networks, which suggests that other groups serve to funnel information towards the formal party.

Why does the influence of Congressional parties fluctuate over time? Building on prevailing answers, we develop a model, Strategic Party Government, which highlights the electoral motives of legislative parties and the strategic interaction between parties. We test this theory using the entire range of House and Senate party behavior from 1789 to 2000 and find that the strategic behavior of parties complements members' preferences as an explanation for variation in party influence. Specifically, the strongest predictors of one party's voting unity are the unity of the opposing party and the difference between the parties in the preceding year. Moreover, we find strong links between party behavior in Congress and electoral outcomes: an increase in partisan influence on legislative voting has adverse electoral costs, while winning contested votes has electoral benefits.