(CNN) The Supreme Court confirmation battle that President Donald Trump triggered with his nomination of Brett Kavanaugh on Monday night may shine a harsh spotlight on the Senate's historic bias in favor of small states.

Kavanaugh could be confirmed by a narrow Senate Republican majority rooted in the nation's smaller states over the virtually unified objections of a Democratic Senate minority strongest in the largest states. Kavanaugh in turn could cement a Republican-appointed Supreme Court majority that would control America's legal framework for years -- regardless of how much of the nation's future population and economic growth flows into the largest states.

The Senate's bias toward small states isn't new: An extended standoff over the issue nearly derailed the convention that wrote the Constitution. Yet the small-state bias may now be more relevant than ever, because it aligns more precisely than at earlier points in American history with the tectonic forces separating the two parties, including urbanization, racial and religious diversity, and the transition to an information-based economy. As small and large states separate even further along those dimensions in the years ahead, the constitutional compromise that provided each state two senators -- in a narrow vote held 231 years ago next week -- could provoke growing tension.

"The Senate diverges wildly from (the principle of) one person one vote," says Frances Lee, a professor of government and politics at the University of Maryland and co-author of the book "Sizing Up the Senate: The Unequal Consequences of Equal Representation." "That's been true since the start, from the very beginning. But it matters more when large and small states differ in a way that is highly relevant for party politics."

In the Senate, the parties don't entirely sort across the large state, small state continuum. Republicans currently hold all the Senate seats across the large and growing Sun Belt states of North Carolina, Georgia, Texas and Arizona -- though Democrats are growing more competitive in each of them. Democrats in turn remain strong in smaller New England states including Maine, New Hampshire, Vermont and Rhode Island. Most of the Rust Belt's big population centers are perennial battlegrounds between the parties, including Michigan, Ohio, Pennsylvania and Wisconsin. Though Trump carried all four in 2016, Democratic senators in each of them are now considered solid favorites for re-election in November.

Big states v. small states

But generally, the Republican Senate coalition is centered on smaller states, while Democrats rely relatively much more on the largest states. Republicans now hold 35 Senate seats and Democrats just 25 across the 30 smallest states. Democrats in turn hold 24, and Republicans just 16, Senate seats in the 20 largest states. Put another way, about half of the Democratic senators represent the 20 largest states, while over two-thirds of the Republicans represent the 30 smallest states.

The contrast between the two Senate coalitions emerges even more clearly when looking at the total population of the states each side represents. One way of measuring the difference is to assign half of each state's population to each senator. Measured that way, the 51 Republican senators now represent about 143 million people, according to the latest Census Bureau state population estimates. The 49 Democratic senators represent about 182 million people, nearly 40 million more. That's about 2.8 million people per Republican senator and 3.7 million people per Democratic senator.

Some analysts might argue that comparison overstates the difference, because California alone accounts for almost 40 million people in the Democratic ledger. But Texas puts 28 million people in the Republican column. Eliminating the largest state on each side still leaves the Democratic senators representing nearly 30 million more people than their Republican counterparts.

If every Republican votes for Kavanaugh, every Democrat votes no and Arizona's ailing GOP Sen. John McCain doesn't vote, as is likely, the senators opposing the choice would represent over 42 million more people than those supporting it.

The sheer disparity in size between the largest and smallest states is the most visible source of questions about the Senate's democratic legitimacy. That divergence is sometimes summarized as the ratio between California and Wyoming, the largest and smallest states: Each California senator represents nearly 19.8 million people, over 68 times as many as the 290,000 each Wyoming senator represents.

Yet even that contrast, while gaping, probably doesn't capture the central force that could significantly heighten tension over the Senate's structure in the years ahead. The real rub could be the widening divergence between the large and small states, not only in their partisan leanings, but also in their exposure to the most powerful forces reshaping American life in the 21st century.

Critically, the small states tend to be less touched than the large ones by the nation's growing racial and religious diversity. Many of the smaller states remain more white and native-born than the nation overall. Wyoming, the smallest state, for instance, ranks 46th in the share of immigrants in its population and 43rd in the share of its under-18 population that is nonwhite. North Dakota and South Dakota, also in the five smallest states, rank 46th and 43rd respectively in immigrant population, and 42nd and 38th in the nonwhite share of their youth population. Montana and Maine, among the 10 smallest states, rank in the bottom 10 on both categories as well. Arkansas, Kansas, Nebraska, West Virginia, New Hampshire, Vermont and Idaho are among the other small states that rank relatively low in both categories too.

Minorities have less representation in Senate

David Shor, a senior analyst at Civis Analytics, a Democratic-oriented data consulting firm, has quantified how the Senate has increasingly diluted the electoral impact of minority voters over time. Using a statistical technique that compares the minority share of the population in each state to the minority share of the nation's overall population, he found that minority voters are more underrepresented in the Senate today than at any point since 1870. Projections by Robert Griffin of the nonpartisan Public Religion Research Institute show that minority underrepresentation is on track to widen further for at least the next 40 years as the nation grows more diverse.

The reason for this growing gap, Shor explains, is that the minority population, particularly immigrants and their children, are concentrating in the largest states already disadvantaged by the Senate's structure, while the predominantly white and smaller states that gain under the rules are diversifying much more slowly. "The issue at a high level is that most growth in the nonwhite population has been concentrated in large states like California, New York and Florida," Shor says.

That means the racial implications of the Senate's small state bias will only grow as the US continues its transition into a majority nonwhite nation through the next quarter century or so. Because that growing nonwhite population is concentrated in relatively fewer states, their influence in the Senate will be enduringly constrained. "The Senate is the last redoubt of white voting power," Shor says. "You have a small group of white rural states ... that are going to have an enormous amount of power, not just over judges, but over vetoing legislation."

Beyond race, other factors are separating the large and small states. The small states tend to be more rural (albeit with some notable exceptions, such as heavily urbanized Rhode Island, Nevada and Delaware), according to census figures analyzed by The Daily Yonder, a website that focuses on rural issues. Smaller states, with very few exceptions, tend to rank lower in the share of their jobs that require a high level of digital skill, a key measure of engagement with the information economy, according to analysis by the Brookings Institution's Metropolitan Policy Program. And even as white Christians have fallen to just over two-fifths of the nation's population, they remain a considerably larger share in many of the smaller states, such as West Virginia, South and North Dakota, Maine, Nebraska, Kansas, Arkansas and Idaho, according to surveys by the PRRI.

Small state advantage extends through US government

All these dynamics now intertwine to produce a Senate that is structurally tilted to advantage the portions of America least touched by -- and in many ways most hostile to -- the big social and economic changes remaking American society. Because of the Senate's role in determining Electoral College votes and confirming justices, its bias toward those states reverberates through those dimensions of political power as well.

"The fact that the racial divide is so deep between the parties, and the urban-rural divide is so deep between the parties, overlaps in problematic ways with the bias in Senate representation," says Lee. "And that bias in Senate representation is also reflected in the Electoral College and in the composition of the court because it is the Senate's job to confirm nominations. So it's all linked."

James Madison, the Constitution's principal architect, bitterly opposed equal representation for every state in the Senate; the dispute over population-based versus equal Senate representation proved the most difficult for the framers to resolve. (As Lee notes, equal representation in the Senate was decided only on a 5-4 vote of the states, with Massachusetts' delegation divided, on July 16, 1787.)

Madison viewed equal Senate representation as unfair to voters in the largest states, but even he did not imagine that small and large states would consistently diverge in so many ways -- not only in their political preference but also in their social and economic structure. As Lee and her co-author, Bruce Oppenheimer, recount in "Sizing Up the Senate," Madison tried to assuage small state fears by noting that the era's largest states -- Massachusetts, Virginia and Pennsylvania -- were wildly different in their religions, manners and agricultural economies.

"Was a Combination to be apprehended from the mere circumstance of equality of size?" Madison insisted. "Experience suggested no such danger."

Even today, "equality of size" doesn't ensure that states lean the same way politically. But that sorting by size seems likely to accelerate as Democratic-leaning minority groups and whites working in the information economy concentrate in the largest states, and Republicans grow more dominant among blue-collar, older, rural and religious whites who predominate in smaller states. Over time, that could enlarge the number of voices, like Shor, openly questioning whether the elements of the American political structure that advantage small states -- the Electoral College and the two-senators-per-state rule -- are systematically benefiting the groups and regions that embody America's past over those forging its future.

"We have an electoral system that is structurally biased against this coalition at every level of government," he frets.

Those complaints, for now, remain at the edge of political debate. But given the intense polarization of modern American politics, it's not difficult to imagine that changing sooner rather than later. For instance, if Trump lost the popular vote again in 2020 yet squeezed out a second Electoral College win, that institution would surely face more intense scrutiny. More immediately, a confirmation battle in which a Republican Senate coalition rooted in smaller, mostly white states enshrines a lasting Supreme Court majority over the objections of a Democratic coalition centered in larger, more diverse states could also provoke more questions about the Senate's imbalances.

"The pressures are latent but it's not yet manifest in our politics," Lee says. "The thing to watch for is the extent to which politicians begin to question the fairness of the system. You need to see more of that before the system's legitimacy is in peril."