Campaign spending by incumbents has surged since 1972, especially in districts where the voter base is not strongly aligned with their party.

In these marginal seats, voters might be swayed by an incumbent's specific legislative record but are unlikely to support candidates who merely reflect the average party member. This phenomenon occurs because political parties have developed increasingly clear voting patterns over time — a more cohesive and precise brand identity — making it easier for voters elsewhere to predict how any given candidate will behave.

However, this same clarity creates challenges in marginal districts: incumbents must now invest significantly more money to attract the undecided or party-switching votes that might be receptive to their particular policy stance. This counterintuitive finding emerges from a formal economic model and is tested using historical campaign data spanning four election cycles (1972-2008).

The Core Argument: More precise party branding forces marginal incumbents into higher spending campaigns.

Methodology Insight: The analysis connects evolving party structures to increased electoral costs for individual candidates in competitive districts.

This research reveals that the growing clarity of partisan identities, while making elections more predictable overall, paradoxically creates a market inefficiency at district margins — requiring incumbents to spend beyond what their specific performance might otherwise justify.