Rob Richie and Andrea Levien have written this article for Presidential Studies Quarterly. Here is the abstract:
The United States has reached an unprecedented level of inequality in presidential elections. In 2012, only 10 states drew the major party presidential candidates for postconvention campaign events, and those same 10 states attracted 99.6% of all general election television advertising spending by the campaigns and their allies. The remaining 41 spectator states (counting the District of Columbia) included all 38 states that had been similarly overlooked in 2008. This article details these inequalities and their roots in state statutes allocating electoral votes on a winner-take-all basis. It argues that states should end this inequality by enacting the National Popular Vote interstate compact, which would ensure that it is the popular vote in all 50 states and the District of Columbia that determines who becomes the president.