Sunstein's 'republic of reasons' argues that a well-designed constitution enables citizens with opposing ethical and religious commitments to reach agreement where agreement is necessary, while making it unnecessary to agree when agreement is impossible. Unlike pure deliberative democracy, which assumes reasoned discourse produces consensus, Sunstein acknowledges deep pluralism and focuses on institutional design—constitutional structures that promote deliberation without demanding uniformity. His approach is pragmatic: constitutions should reduce the costs of political disagreement by creating spaces for 'incompletely theorized agreements' on particular outcomes without requiring consensus on underlying principles.

Sunstein proposes three approaches to constitutional interpretation. Traditionalism grounds the document's meaning in long-standing social practices, not necessarily the Founding generation's views; populism insists judges should respect contemporary public opinion; cosmopolitanism looks to how foreign courts address constitutional questions, suggesting meaning depends partly on what other nations do. All three deploy a 'many minds' argument—better decisions result when many perspectives are considered. Sunstein doesn't endorse any single approach absolutely but sketches contexts where each provides legitimate interpretive guidance.

Both theorists recognize that fundamental constitutional change can occur outside Article V amendments, but they diverge significantly. Ackerman's 'constitutional moments' are rare, epochal episodes of sustained popular mobilization producing new constitutional regimes. Sunstein's framework is more expansive and granular: he distinguishes between full 'constitutional moments' and 'constitutional mini-moments'—smaller shifts that cumulatively reshape constitutional understanding. His 2025 work *Founding and Refounding* outlines seven concrete presidential initiatives that could constitute a new constitutional moment, emphasizing executive action rather than Ackerman's focus on congressional-statutory transformation.

Sunstein's anticaste principle holds that the Constitution forbids government action that creates or perpetuates second-class citizenship based on immutable characteristics like race, gender, or sexual orientation. Unlike strict equality doctrines that demand identical treatment, the anticaste principle focuses on systemic subordination—it asks whether a law or practice casts any group into an inferior social status. Sunstein argues this principle can justify affirmative action, same-sex marriage rights, and sex equality protections without relying on suspect classification doctrine alone. The principle is grounded in the Fourteenth Amendment's historical purpose of eradicating caste systems like slavery and Jim Crow.

From 2009 to 2012, Sunstein administered the White House Office of Information and Regulatory Affairs, overseeing federal regulations with net benefits of approximately $150 billion. This experience grounded his abstract theories in practical governance—he witnessed how cost-benefit analysis, nudges, and administrative procedure actually function. His later work emphasizes 'humanizing' cost-benefit analysis by focusing on unquantifiable human consequences and demonstrates how behavioral insights can improve regulatory design while respecting constitutional constraints. The experience reinforced his conviction that constitutional theory must engage with real-world policymaking, not remain purely academic.

Sunstein defends a form of judicial minimalism where courts should not decide unnecessary questions when resolving cases. Unlike simple judicial restraint (deferring to other branches), minimalism is a theory of adjudicative scope: decide narrowly, leave broader questions for democratic resolution, and avoid sweeping constitutional pronouncements. This approach respects democracy by preserving space for political deliberation while protecting individual rights through case-by-case reasoning. Sunstein argues minimalism is particularly appropriate in a self-governing society of free people because it reduces the stakes of judicial decisions and prevents courts from becoming super-legislatures.

In *The Partial Constitution* (1993), Sunstein argued that the Constitution as currently interpreted is 'partial'—it illegitimately privileges the status quo by treating government inaction as constitutionally neutral while scrutinizing action. When courts ask whether government action violates rights, they implicitly compare it to a baseline of no government action. But this baseline is itself a choice that favors existing distributions of wealth, power, and opportunity. Sunstein argues courts should instead ask whether government action (or inaction) systematically disadvantages vulnerable groups. His critique reshaped constitutional adjudication by exposing the hidden normative commitments embedded in seemingly neutral judicial tests.

Sunstein's 'libertarian paternalism'—using nudges to steer behavior while preserving choice—raises constitutional questions about government power, liberty, and democratic accountability. Nudges are 'freedom-preserving' because individuals can easily opt out, avoiding traditional paternalism concerns. But critics ask: when does nudging become manipulation, and does it violate due process or equal protection? Sunstein engages these questions by arguing that choice architecture is inevitable—there is no neutral design—so government should design choices to improve welfare while respecting constitutional limits. His work has influenced nudge units worldwide and sparked ongoing debate about the constitutional boundaries of behavioral governance.