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.

A healthy degree of party unity among Democrats and Republicans has deteriorated into bitter partisan warfare.

The increase in straight-ticket party voting in recent years means that competitive congressional races can tip one way or the other depending on the showing of the candidates at the top of the ticket.

With the parties at virtual parity and the ideological gulf between them never greater, the stakes of majority control of Congress are extremely high.