The cold war between red and blue states is escalating to a dangerous new level. Under the piledriver pressure of President Donald Trump’s bellicose second term, the red and blue blocs are moving from separation to confrontation.

The first stage in this unraveling has been divergence on state policy, particularly around social issues.

From the 1960s through the early 21st century, the general trend of American life — advanced through both Supreme Court decisions and congressional legislation — had been to nationalize more rights and to restrict the ability of states to infringe on those rights. But red states, supported at key moments by the Republican-appointed Supreme Court majority, have moved steadily since then to reverse that “rights revolution” — at least on rights they dislike.

Virtually every Republican-controlled state has retrenched rights for transgender young people and imposed new restrictions on voting access, while most have also banned abortion and DEI programs; censored discussion of race, gender and sexual orientation in K-12 schools; and made it easier for critics to ban books. Almost no Democratic-controlled states have done any of those things. Conversely, red states have expanded“religious liberty” exemptions from anti-discrimination and other laws and expanded gun rights (such as authorizing gun owners to carry concealed weapons without a permit) in ways very few blue states have followed.

The result is the biggest gulf between the rights available in some states and denied in others since the era of Jim Crow segregation.

The next step up the ladder of separation has been alliance, as red and blue states have joined in unprecedented ways to resist the national agenda of the other party.

This instinct first manifested soon after 2000 in the proliferation of lawsuits from coalitions of state attorneys general against the policies of presidents from the other party.

More recently, states in each bloc have also joined forces to directly counter the policies of a president from the other party. When Trump in 2017 withdrew from the Paris climate accord, Democratic governors launched the U.S. Climate Alliance explicitly to maintain momentum behind the carbon-reduction goals Trump renounced. During Biden’s presidency, about a dozen red states sent law enforcement or National Guard forces to join Texas Governor Greg Abbott’s “Operation Lone Star,” which pursued a highly militarized approach to border enforcement that Biden did not support. The latest reflection of this impulse is the public health alliance that California, Oregon and Washington announced last week (and the similar collaborative that nine blue East Coast states are formulating) to counter Robert F. Kennedy Jr’s moves to undermine vaccine access as head of Health and Human Services.

The alliance strategy implicitly shifts states’ vision about where they owe their loyalty. Rather than considering themselves part of a unified national republic, it encourages states to primarily view themselves as part of a red or blue faction locked in conflict with the other side.

Trump, as he often does, has pushed that vision to a dark extreme through his pressure on red states to gerrymander more Republican seats in the House of Representatives. In essence, Trump is arguing that the principal obligation of Republican governors and legislators is not to provide fair elections that accurately reflect their constituents’ preferences, but to contribute by any means necessary to the entrenchment of national Republican power. Blue states, inevitably, are responding in kind.

Jake Grumbach, a University of California at Berkeley political scientist, says the tendency of states to work within their party’s “national team” subverts James Madison’s belief that federalism would, like checks and balances in the federal system, provide protection against tyranny. In particular, Trump’s pressure on red states to alter their elections so he can maintain national power “is the most anti-Madisonian notion of all time,” Grumbach told me. “He’s enlisting every part of federalism for this national goal of essentially [imposing] national authoritarianism.”

As loyalty to the national team has exerted more influence on state decisions, it’s been a distressingly small step toward the latest, and most ominous, form of separation: the eruption of direct conflict between red and blue states.

This instinct surfaced under Biden when the GOP governors of Texas and Florida shipped undocumented immigrants into blue cities without notice or permission. It ripples through the retaliatory cycle of red-state restrictions on abortion and gender transition care, the “shield laws” blue states have passed to protect physicians within their borders, and the responses from red states trying to punish those physicians (the latest of which is the Texas “bounty hunter” law Abbott is expected to sign shortly.) And it animates Oklahoma’s new requirement that teachers relocating from other states pass an “America First” ideological test before they can teach in public schools.

Trump and his advisers are again taking this trend to a dark extreme by suggesting he may deploy National Guard forces from red states into blue ones over the objections of local officials. Though Abbott has denied that Texas National Guard forces are mobilizing to imminently roll into Chicago (as Illinois Governor JB Pritzker charged last week), Abbott’s spokesperson has said that Texas is “ready, willing, and able to deploy all necessary resources to clean up the streets of Chicago should President Trump call upon us to do so.” It’s a measure of how far the nation has already pulled apart that it does not seem impossible that unwelcome forces from a former Confederate state could soon occupy ground in the home state of Abraham Lincoln, the president who guided the Union through the Civil War.

On paper, Trump faces a Catch-22 if he tries to send red state troops into blue states, says Joseph Nunn, a counsel in the liberty and national security program at the Brennan Center for Justice. Guard forces from one state can enter another state over their governor’s objections only if the president has federalized them, he says; but once the president federalizes a state National Guard, it is subject to the Posse Comitatus Act’s prohibition on engaging in domestic law enforcement.

That barrier may not be as impregnable as it seems, however. In the case involving Trump’s federalization of the California National Guard, the administration argued that courts cannot enforce the Posse Comitatus Act by ordering the president to end a military deployment. Charles Breyer, the district court judge, emphatically rejected that argument, but Nunn worries the Republican-appointed Supreme Court justices may accept Trump’s claim. At that point, Nunn says, “the most important restriction” on domestic use of the military could become “unenforceable.” Those fears seem especially urgent after Monday’s decision by the GOP Supreme Court majority essentially providing a blank check for Trump’s aggressive immigration enforcement.

In Trump’s vision, the widening conflict among the states is just a way-station: He’s employing every means of national power (including lawsuits, funding threats and the use of troops) to force the blue states to adopt the conservative red state policies they have rejected. In the process, he’s imposing the greatest strain on the nation’s fundamental cohesion since the Civil War. History doesn’t repeat, so secession, much less armed conflict, still seems the province of dystopian fantasy. But anyone who assumes the mounting hostility between red and blue states could not produce some other crisis is not paying attention.

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This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Ronald Brownstein is a Bloomberg Opinion columnist covering politics and policy. He is also a CNN analyst and previously worked for The Atlantic, The National Journal and the Los Angeles Times. He has won multiple professional awards and is the author or editor of seven books.

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