If the USA had direct plurality election of the president, what effect on the party system?

I know the 2020 election result–assuming the Senate majority remains Republican–has ended any chance of serious electoral reform passing for the foreseeable future. But what if the National Popular Vote (NPV) compact were enacted? If there were no other reforms, the compact would result in the US President being elected by direct nationwide plurality.

Given the way assembly and presidential party systems work together in systems with powerful directly elected presidents, just changing to direct election in the USA could open up the wider party system in a way fully consistent with expectations from its existing electoral system. It is likely that direct election would lead to more presidential candidates winning votes, and that, in turn, would potentially lead to more parties in House elections, because the House party system is probably currently being restrained by how the presidency is elected more than by how the House itself is elected.

The House electoral system has seat product of 435. (The seat product of a single-tier electoral system is its mean district magnitude, times the assembly size.) Based on the Seat Product Model, the expected party system in the US House would have an effective number of seat-winning parties of around 2.75, on average, and a largest party averaging around 46.8% of the seats (about 204 seats). Of course, the actual party system has an effective number just below 2.0 and a largest party always above 50% of the seats. Do not blame the electoral system for the absence of other parties in American national politics. Even with single-seat plurality (in a few states, majority), the electoral system for the House should be expected to support more parties than what we actually have.

If we look at the worldwide dataset of presidential elections that Rein Taagepera and I analyze in Chapter 11 of Votes from Seats, the mean total for winning presidents under nationwide plurality is 48%. That is, of course, below the long-term average for US presidents, which is 52%, although it has trended downward since 1992 and averages around 49% over the past three decades, suggesting there is indeed some pent-up demand for more options. The leading presidential candidate typically wins more than the 48% that is the average in countries using direct plurality because the multi-seat plurality rule used at the state level in the electoral college normally suppresses third parties. And, unable to attract many votes in presidential contests, sustained party organizations beyond the top two are lacking. If they existed, they likely would compete for House seats as well.

It just so happens that a switch to direct plurality election of the president would be pretty consistent with what the existing House electoral system should be yielding! The estimates we have are: A president winning 48% on average (roughly what Hillary Clinton won in 2016, though with the electoral college that was not good enough); A largest party in the House having 47% of the seats. Based on other formulas in the Seat Product Model (SPM), the expected vote share of the largest party in the House then would be 42.5%, for an implied effective number of vote-earning parties of 3.13.

While it would be nice to have proportional representation of some sort for the House, it actually is the case that just changing to nationwide plurality for the presidency–as the NPV would produce–might be sufficient to “unleash” the House seat product and bring about a relatively more multiparty, but not significantly fragmented, House party system.

A quick comparative check of the data is in order, to see how these estimates compare to other countries’ experience. Across 117 presidential and semi-presidential systems (including, for the latter, only those with “strong” presidents), the mean share for the first-round or sole-round leading presidential candidate is 46.64% and the mean vote share for the largest assembly party in those same cases is 40.43%. Restricted to just pure presidential systems and those that elect their presidents by plurality (only 25 observations) we have 44.88% and 40.95%, respectively. So 42.5% for the largest vote share in US House elections is within the ballpark of other presidential systems’ observed experience; the set of cases from which I just reported average values has a mean seat product of 934.5, which is obviously higher than the US House’s seat product, and so they should be expected to have higher average fragmentation (smaller leading party) than the USA.

Additionally, Taagepera and I also have a model in Votes from Seats to estimate the effective number of presidential candidates (Np) from the assembly electoral system. It is Np=1.44[(MS)1/4 +1]1/3 (where M is the district magnitude–here 1, obviously–and S is the assembly size). For the US, this yields Np=2.55. We did not try to predict the vote share of the leading presidential candidate, but a rough approximation from that effective number would be 49.5%. Thus, roughly 48-50% for the president, on average, from direct plurality, plus a largest party in House elections in the ~43% range, seem like good educated guesses if the US were to change to direct plurality, by way of the NPV, even without any change in the House electoral system.

Given that reform to PR normally follows, rather than leads, an increase in vote share to parties other than the majors, it is even possible that the NPV’s anticipated effect on the wider party system could generate momentum towards House electoral reform. But that is beyond the scope of this planting, which was simply intended to show that the currently under-fragmented House (according to the SPM) could be brought in line with expectations simply by making presidential elections direct via plurality.

A couple of caveats: First, the exercise here reveals that the multi-seat plurality system of the current electoral college could be a major drag on the party system at the moment, preventing the House from having the party system its seat product could support. However, we should not ignore the Senate. Given that the Senate is a co-equal chamber, parties need to organize with this body in mind, as well as with an eye towards seat-winning potential in the House. And the Senate seat product is ridiculously small. Even if it were taken to be 100, based on the Senate’s total size, that would be small–roughly the size of New Zealand’s before its electoral reform in the 1990s. However, it is worse than that: I think its seat product actually should be coded as 33, as that is the normal number of seats at stake in any given election. And if we run the SPM on a seat product of 33, we get an expected largest party seat share of 65% (!). Obviously, the actual is already normally well below that, at least in recent times. So that suggests that the more “permissive” House electoral system is already helping keep the Senate less dominated by one party than the Senate electoral system in isolation would.

The second caveat is that primaries also reduce party-formation incentives somewhat. But my working assumption is that ideological groups within the existing parties would bypass primaries for president if the latter were elected nationwide, and that the resulting new parties would want to show their flag in House elections, too, under such a scenario. Yes, of course, single-seat districts make life hard on smaller parties. But note that no single-seat plurality system in the world with a seat product greater than about 100 has a party system as dominated by two parties as the USA has. So small parties can find ways to win local pluralities. They just need to be unleashed. And plurality election of the president would help the House’s existing seat product do its thing.

Electoral reform is not happening soon. The NPV itself is likely off the table for now. Even if sufficient states (totaling at least 270 electoral votes) were to agree to enter into the compact, it presumably would take effect only with the approval of Congress. Thus as long as Republicans control the Senate, its chances are poor. Nonetheless, the issue will not go completely away (I hope!), and it is thus helpful to understand that just this one measure could break the dam of the rigid two-party system for elections to the national legislature, even without any reform of how the House is elected.