Yes, Americans are polarized. But that doesn't prevent wave elections
A popular measure of intra-party loyalty in polls artificially inflates electoral stability and ignores the crucial role that turnout plays in close races
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In a column from late May, Charlie Cook argues the Democratic Party will have a hard time winning a big “blue wave” election this November because it is counting on persuasion among Republicans that may never materialize:
Even while polls show mounting reservations about President Trump, if not downright opposition, that has minimal bearing on Republican voters in the red states and districts that Democrats need in order to flip the Senate or approach a wave election in the House. In this new era for our politics, voters having doubts about a president of their own party is one thing, but voting for the opposition party is something else entirely.
Empirically, Cook shows that the “party loyalty rate” (the percent of Democratic-aligned voters who vote for Democratic candidates, and Republican voters who vote for Republican candidates) is sky-high, meaning (in theory) there are few Republican converts around to supply the party a robust majority in either the House or Senate:
Just 4 percent of Democrats voted for Donald Trump in 2024, precisely the same share of Republicans who voted for Kamala Harris; in each case, 95 percent of each side toed the party line. Four years earlier, both Trump and Joe Biden pulled the exact same 95 percent of their fellow party members. In 2016, the cohesion levels were only slightly lower, with 94 percent of Democrats voting for Hillary Clinton and 92 percent of Republicans for Trump. … There are even fewer defections in midterm elections. In 2018, 97 percent of voters identifying as Democrats backed their side’s candidates; in 2022, it was 98 percent. For the GOP, it was 95 percent in 2018 and 97 percent in 2022.
And to be clear, “party loyalty” when measured like this looks high in polling today, too; it’s not just a product of looking at past election results. A New York Times/Siena poll conducted May 11–15 put Trump’s approval at a second-term low — 37% approving, 59% disapproving. And yet, when you look inside the Republican column, only 5% of self-identified Republicans said they’d vote for a Democratic candidate for Congress. Ninety-two percent said Republican.
So are Democratic hopes for winning a majority dashed? Are polls showing such a large lead for the party a phantom result of optimistic polling that will disappear when people actually cast ballots?
Cook gets a lot right: Party loyalty is high, and split-ticket results have nearly vanished from American politics. There are very few Republican senators from states that vote for Democratic presidential candidates and vice versa. And Democrats genuinely cannot assume that every Trump-disapproving Republican is theirs for the taking; if you look at the survey data, it looks like most, in fact, won’t convert.
But I do think there’s a couple problems with this 95% partisan loyalty statistic. Both issues have the effect of making actual vote-switching between parties sound rarer than it is. As I show in this article, what we really care about is not what percentage of current, self-identified partisans vote for their party’s candidate, but what percent of one candidate’s voters switch sides or fall off in the next election. This sounds like a pedantic distinction, but it has big consequences — I’ll show you what I mean with hard data.
This week’s Deep Dive is a look at why Cook’s way of analyzing party loyalty overstates partisan polarization/partisan sorting. Last week, I ran the math on how many Trump voters Democrats need to win over to win the Senate race in Texas, and the answer came in lower than I think most people expected. Similarly, this week’s post has big implications for imagining what’s possible in future elections.
