The failure of presidents attending the Summit of the Americas to issue a final declaration because they could not agree on whether to invite Cuba to the next meeting represents a disappointing breakdown of the consensus over the founding principle of the Organization of American States: a devotion to freedom and democratic institutions.

This failure calls into question the very nature of the OAS. How can a coalition of countries ostensibly devoted to promoting and strengthening democracy invite Cuba to a meeting of like-minded countries?

Aside from being part of Latin America, the democratic countries of the Western Hemisphere and Cuba have nothing in common.

With its half-century of dictatorship and open contempt for democratic institutions, Cuba represents everything that countries aspiring to freedom reject — no real elections, no freedom of speech or free press, no human rights. In short, it’s the ultimate police state.

Now that Washington’s 50-year policy of isolating Cuba no longer has the same level of hemispheric support it once enjoyed, the Obama administration has its work cut out for it.

This will demand more attention to hemispheric policy than Washington has mustered in recent years, given two wars in other parts of the world and nuclear threats elsewhere.

Cuba’s aging rulers are not about to abandon their lifelong commitment to communism, so Mr. Obama — or whoever succeeds him as president — must offer a strong and unequivocal defense of democracy and human rights, the most glaring failure of the Cuban Revolution.

“Respect for human rights goes to the very heart of democracy,” according to the home page of the OAS human rights agency. If Cuba is “invited” to anything, it should be to explain why it violates common standards of human rights.

If nothing else, the Cartagena summit gave Washington an agenda for the next such meeting. It’s not scheduled to take place until 2015, but it’s not too early to start planning for it.