That’s not just an anecdotal impression. The tools of computational analysis shed light on how wide the chasm has grown.

The three of us recently examined the evolution of constitutional rhetoric on the floor of Congress from 1873 to 2016. We first identified the hundreds of thousands of remarks that referred to the Constitution. We then trained a machine-learning classifier to predict—based solely on the content of the remarks—whether Republicans or Democrats were speaking. If the algorithm finds this task hard to do, it implies that the parties are apt to talk in similar or overlapping ways. By contrast, if the algorithm performs this task with a high degree of accuracy, it implies that the parties are largely talking past each other.

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The results are sobering. Since around 1980, it has become increasingly easy for an algorithm to predict whether any given constitutional remark was made by a Republican or a Democrat. It has likewise become increasingly easy to predict whether the speaker was a conservative or a liberal. By the time Trump took office, the machine was guessing right roughly 80 percent of the time, an all-time high by historic standards.

This result holds up across multiple machine-learning classifiers, multiple measures of algorithmic accuracy, and multiple criteria for what counts as a constitutional remark. Additional tests of the “disjointness” between the parties’ rhetoric point to the same conclusion: To an unprecedented extent, Republican and Democratic members of Congress no longer speak the same constitutional language.

Underlying this polarization of constitutional discourse, we further found, are competing constitutional vocabularies. Terms dating back to the ratification of the original Constitution in the late 1700s have become relatively associated with the Republican Party. For instance, today’s conservatives are more likely to use the phrase Founding Fathers and cite textual provisions such as the First, Second, and Tenth Amendments, emphasizing themes of individual liberty and the autonomy of the states.

Terms from or about the Reconstruction Amendments of 1865–70, on the other hand, have become relatively associated with the Democratic Party. Democrats are more likely to deploy the phrases civil rights and voting rights in particular, emphasizing themes of equality and federal authority. The perennial tension in constitutional law “between the values of the Founding and the values of Reconstruction,” as the law professor Kermit Roosevelt has described it, is today a highly partisan struggle.

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Even more so than the fight over Trump’s tax returns, the ongoing debate over a high-profile Democratic electoral-reform bill shows how this struggle plays out. After House Democrats introduced H.R. 1 in January, Republicans insisted that the bill would “limit Americans’ First Amendment right to political speech” (Senator Mitch McConnell), encroach on “the liberties and powers of the Constitution reserved for the states and the people” (Representative Jeff Duncan), and undermine “the original intent of the Founders” (Representative Barry Loudermilk). Democrats countered that the bill would provide crucial protections for the “constitutional right to vote” (Representative Sheila Jackson Lee) and help redeem “a Constitution that was flawed” at its inception “by not recognizing the full equality of every American” (Senator Jeff Merkley).