Votes in federal elections are cast and counted in a highly decentralized and variable fashion, with no uniform ballots and few national standards.
In the House, Republican prospects have been buoyed by several successful rounds of redistricting, which have sharply reduced the number of competitive seats and given the Republicans a national advantage of at least a dozen seats.
Redistricting is a deeply political process, with incumbents actively seeking to minimize the risk to themselves (via bipartisan gerrymanders) or to gain additional seats for their party (via partisan gerrymanders).
In addition to the decline in competition, American politics today is characterized by a growing ideological polarization between the two major political parties.
Responsibility for overseeing the implementation of election law typically resides with partisan officials, many with public stakes in the election outcome.
But presidential approval also became a surrogate measure of national unity and patriotism.