The claim that America is not a democracy but a constitutional republic is mostly true because the U.S. Constitution explicitly establishes a republic with representative government and does not use the term 'democracy,' although the system incorporates democratic elements such as voting and majority rule.
America is not a democracy. It is a constitution republic.

The United States: Democracy or Republic? - Origins
Source: origins.osu.edu
Key Evidence
The U.S. Constitution guarantees a republican form of government and does not mention democracy explicitly.
origins.osu.eduorigins.osu.eduThe United States: Democracy or Republic?
constitutingamerica.orgconstitutingamerica.orgRepublic or Democracy? Classical History, Republican Governing as Adopted by the...
The system relies on elected representatives rather than direct rule by the people, fitting the definition of a republic.
heritage.orgheritage.orgAmerica Is a Republic, Not a Democracy
constitutionus.comconstitutionus.comIs the United States a Republic?
Democratic elements like voting and majority rule exist within this constitutional framework.
npr.orgnpr.orgIs America a democracy or a republic? Yes, it is : NPR
What the Evidence Shows
The United States is officially a constitutional republic, meaning it is governed by elected representatives under a supreme constitution that limits government powers. The Constitution itself mentions 'republic' but never uses the word 'democracy'.origins.osu.eduorigins.osu.eduThe United States: Democracy or Republic? This distinction is important historically and legally, as the founders intended to avoid what they called 'pure democracy' or direct majority rule without constitutional constraints.
heritage.orgheritage.orgAmerica Is a Republic, Not a Democracy+3 more
However, the U.S. System includes democratic features such as popular elections and majority decision-making within a framework of laws and protections for minority rights.npr.orgnpr.orgIs America a democracy or a republic? Yes, it is : NPR Some sources emphasize that calling America solely a republic without acknowledging its democratic aspects can be misleading or politically motivated.
bunkhistory.orgbunkhistory.org‘America Is a Republic, Not a Democracy’ Is a Dangerous—And Wrong—Argument+1 more
Thus, while it is accurate to say America is a constitutional republic, it is also accurate to recognize it as a representative democracy in practice.