The American Journal of Political Science (AJPS) has created a free virtual issue that has a sampling of articles on midterm elections that have appeared in the AJPS since 2007. This is an excellent initiative aimed at spreading political science work to a broader audience. Below are links to the articles that are temporarily available to all without cost.
Presidential and Congressional Vote-Share Equations
Ray C. Fair
Candidate Valence and Ideological Positions in U.S. House Elections
Walter J. Stone and Elizabeth N. Simas
The Electoral Costs of Party Loyalty in Congress
Jamie L. Carson, Gregory Koger, Matthew J. Lebo and Everett Young
District Complexity as an Advantage in Congressional Elections
Michael J. Ensley, Michael W. Tofias and Scott De Marchi
The Check Is in the Mail: Interdistrict Funding Flows in Congressional Elections
James G. Gimpel, Frances E. Lee and Shanna Pearson-Merkowitz
Candidate and Party Strategies in Two-Stage Elections Beginning with a Primary
James Adams and Samuel Merrill III
The Campaign Value of Incumbency: A New Solution to the Puzzle of Less Effective Incumbent Spending
Kenneth Benoit and Michael Marsh