A political shift decades in the making explains Trump’s grip on Congress

A recent analysis suggests that Republican members of Congress support Donald Trump’s agenda not primarily out of fear, but because they now share the exact same voters. The research indicates that a decades-long geographic shift has perfectly aligned the party’s presidential and congressional electoral bases, leading to shared policy goals. These findings were published in PS: Political Science & Politics.

In the American political system, the Constitution sets up a natural rivalry between the president and Congress. Because the president is elected nationally and members of Congress are elected by specific states and local districts, the two branches answer to different groups of people. Recently, commentators have accused Congress of abandoning this independent role and surrendering its power to Trump. The common explanation is that lawmakers are intimidated by his popularity and his willingness to attack dissenting Republicans on social media.

“Is democracy relevant in America? The media presents congressional compliance with Trump as due to fear of him. One man has intimidated Congress and abolished the separation of powers,” study author Jeffrey M. Stonecash, a Maxwell Professor Emeritus at Syracuse University, told PsyPost.

“While there is a grain of truth to that, what we are witnessing is primarily the result of a lengthy realignment that has created a geographical overlap of presidential and congressional electoral bases,” he added. “That base is conservative socially and economically.”

However, political scientists have documented a massive shift in American voting behavior over the past several decades that provides an alternative explanation. A 2018 book indicated that voters across the country have largely stopped splitting their tickets, meaning they increasingly choose the same political party for both congressional and presidential races.

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This trend was accompanied by intense geographic sorting. A 2017 book explained that the geographic divide between rural and urban voters has organized local congressional districts into deeply partisan camps that mirror national party lines.

Because of this geographic sorting, the priorities of local lawmakers have merged with those of national leaders. A 2015 study documented how rising polarization reshaped relations between Congress and the White House, making party allegiance the dominant factor in whether lawmakers support the president. At the individual level, a study covered by PsyPost in 2024 indicated that alignment with the Make America Great Again movement of the Republican Party is now a stronger predictor of primary election success than traditional advantages like holding office.

Stonecash’s new research builds on these findings. He investigated how a historical geographic realignment created the modern Republican base. The study suggests that Republican lawmakers back Trump because their local voters now share the exact same priorities as his national base, a situation that has not existed to this degree since 1952.

To understand this shift, Stonecash analyzed election data spanning from 1952 to 2024. He focused on tracking the overlap between states and districts that voted for a Republican presidential candidate and those that elected a Republican member to the House of Representatives or the Senate.

A major part of the analysis involved tracking 19 specific states mostly in the South and Western interior. In the 1940s, these states provided almost no support to Republican presidential candidates. Over time, as the Republican Party adopted more socially conservative platforms, these states slowly flipped. By analyzing decades of voting data, Stonecash mapped how Republican presidential candidates began winning these states long before Republican congressional candidates did.

The researcher found that for decades, Republican presidents struggled with a mismatch between their electoral base and their congressional party. Presidents like Richard Nixon, Ronald Reagan, and George H.W. Bush either did not have a Republican majority in Congress, or they had majorities that included many lawmakers elected in districts won by Democratic presidential candidates. This meant Republican presidents had to negotiate with members of their own party who answered to more liberal or moderate voters.

The data indicates that Trump currently enjoys a historically rare level of geographical overlap with his congressional party. In the years from 1952 to 2012, when a Republican presidential candidate won a specific congressional district, Republican House candidates won 63.6 percent of those districts. During Trump’s three elections in 2016, 2020, and 2024, that overlap jumped to 96.7 percent.

This means that almost every House district Trump wins also elects a Republican representative. In 2016 and 2024, Trump entered office with a majority in the House of Representatives, and very few of those Republican members came from districts that voted for the Democratic presidential candidate. Dwight D. Eisenhower was the last Republican president to share this specific advantage.

The pattern is similar in the Senate. Before Trump, Republican Senate candidates won an average of 55.5 percent of the time in states carried by the Republican presidential candidate. Under Trump, that average rose to 83.3 percent. In his second term, Trump has a Senate majority with 52 seats coming directly from states that he actively won.

The findings suggest that congressional deference to Trump is driven by shared constituencies rather than pure intimidation. The lawmakers in Trump’s congressional party answer to the exact same voters that he does. According to recent polling data highlighted in the study, Trump’s approval ratings remain highly positive among Republicans in his winning states, even when his overall national approval drops.

“Members of Congress come from states and districts that Trump won and where voters liked what Trump was presenting,” Stonecash explained. “There is considerable agreement with what Trump is doing. Members of Congress may sometimes dislike his style and abrasiveness, but they like where he is taking the country.”

Because these lawmakers rely on those same voters to keep their jobs, supporting the president’s agenda makes logical political sense. The analysis provides evidence that Republican members of Congress are not abandoning their institutional roles, but rather using a unified electoral base to pursue shared conservative goals.

“The important matter is that we are not just witnessing a lone actor imposing policies only he supports, but a party acting in a roughly unified manner,” Stonecash noted. “Over decades a party built a base to counter liberals. For those troubled by the current administration, the answer is not just to seek to limit Trump. An opposing party needs a base to counter that which the Republican Party has created.”

As with all research, there are a few things to keep in mind. The study relies on macro-level election data, which reveals broad historical patterns but does not measure the internal motivations or private fears of individual lawmakers. While the data shows that shared voters encourage cooperation, it does not rule out the possibility that social media pressure or fear of primary challengers also plays a role in keeping lawmakers in line.

Additionally, the analysis groups states and districts into broad categories based on historical voting trends. This approach provides a large-scale view of political realignment but might smooth over unique local dynamics within individual districts. The data also focuses heavily on the 19 southern and western interior states that shifted from Democratic to Republican, meaning the narrative of realignment is mostly concentrated on these specific regions.

Going forward, the researcher emphasized that understanding this historical context is key to grasping modern polarization. “How this realignment unfolded is presented in The Transformation of the Republican Party,” he said. “The consequences of this realignment will be with us for decades and there is much to understand about its long-term effects on American politics.”

The study, “Political Realignment and Congressional Deference to Donald Trump,” was authored by Jeffrey M. Stonecash.