Doug Mataconis wonders why there haven’t been more ideological insurgencies against sitting presidents recently, and proposes part of an answer:

Some of this, I suggest, can be attributed to the fact that both of our major political parties have become far more rigid and ideological than they might have been in the past. The idea of a Ted Kennedy mounting a primary challenge against his party’s President is seems like an alien concept today.

The decline in significant intra-party primary challenges points towards the possibility that the major parties have become more ideologically uniform (though not necessarily “more rigid and ideological”), but that isn’t an entirely satisfactory answer. Even if one or both parties had become more ideologically uniform than they were in the past, politically weakened presidents would still invite intra-party challenges. After all, challenges for party leadership aren’t always driven by ideological divisions.

Kennedy’s challenge to Carter was partly a product of Carter’s relative lack of support within his own party and his antagonistic relationship with Congressional Democrats. Similarly, Ford was in a weak position within his party as an unelected president with no strong ties to the party’s growing conservative wing. The examples of the Reagan and Kennedy challenges also served as warnings in later years that trying to deny a sitting president re-nomination simply made it that much easier for the other party to prevail in the general election.

Since primary challengers have fallen short of defeating the sitting president, the effort seems both futile and risky. There have been major disagreements between the incumbent and many of his most ideological supporters, but ideological voters are also mostly strong partisans and tend to set aside their disagreements to keep their party in power. The disagreements with the incumbent have to be considered significant enough to merit the risk of losing control of the Presidency, and the conditions in the country (or fortunes in a foreign war) have to be bad enough to make disagreements seem important enough to justify taking that risk. When those conditions are present, incumbent presidents face challengers or choose not to seek re-election at all. It’s those conditions rather than the ideological factor that account for these challenges, and those conditions have been absent in the last three re-election cycles.

When the time for primary challengers to appear came in 1995, 2003, and 2011, there was no one in the presidential party that had any serious thought of running against the incumbent. Under different circumstances, Bush might have had to face a primary challenge because of his domestic agenda, and had he been seeking re-election two years later he almost certainly would have had to face one, but events and timing worked in his favor. The public had not yet soured on Bush’s disastrous decision to invade Iraq as they would later, his party was largely united behind that decision, and he was still benefiting from the post-9/11 surge in his approval rating. Far from agitating for a challenge against Bush, most movement conservatives were singing his praises and rallying around him. In each of the last three cases, when it came time for re-nomination the incumbent president was benefiting from a growing economy, however anemic that growth might be, and a party that was largely unified behind the president and strongly in agreement that the other party should not be trusted with power.

Something else to bear in mind is that it has been fairly normal for one party or the other to hold the White House for at least eight years. Because of death or resignation, it hasn’t always been the same person occupying the White House, but a party usually doesn’t lose the public’s support quickly enough to be limited to a single four-year term in power. All other things being equal, we should expect the same party to retain control of the White House for two consecutive terms.