“The United States is…a warning rather than an example to the world.”

Edward Snowden accuses US of illegal, aggressive campaign in his first appearance in the airport http://www.guardian.co.uk/world/2013/jul/12/edward-snowden-accuses-us-illegal-campaign, published by The Guardian 12 July 2013.
Interview with Glenn Greenwald, 6 June 2013, Part 2

Hossein Salami (2020) cited in: " Iranian general warns of retaliation if US threats continue https://www.taiwannews.com.tw/en/news/3865471" in Taiwan News, 27 January 2020.

26 June 2003 http://www.politicalposts.com/news/index.asp?id=180606 http://www.sltrib.com/2003/Nov/11212003/commenta/commenta.asp.
2000s, 2003

Variant: If you can't be a good example, you'll just have to be a horrible warning."
-Gwen Goodnight
Source: Faking It

2014, Statement on Cuban policy (December 2014)
Context: To the Cuban people, America extends a hand of friendship. Some of you have looked to us as a source of hope, and we will continue to shine a light of freedom. Others have seen us as a former colonizer intent on controlling your future. José Martí once said, “Liberty is the right of every man to be honest.” Today, I am being honest with you. We can never erase the history between us, but we believe that you should be empowered to live with dignity and self-determination. Cubans have a saying about daily life: “No es facil” –- it’s not easy. Today, the United States wants to be a partner in making the lives of ordinary Cubans a little bit easier, more free, more prosperous.
To those who have supported these measures, I thank you for being partners in our efforts. In particular, I want to thank His Holiness Pope Francis, whose moral example shows us the importance of pursuing the world as it should be, rather than simply settling for the world as it is; the government of Canada, which hosted our discussions with the Cuban government; and a bipartisan group of congressmen who have worked tirelessly for Alan Gross’s release, and for a new approach to advancing our interests and values in Cuba.

2000s
Variant: The world has always been more impressed by the power of our [America's] example than by the example of our power.
Context: Former U. S. president Bill Clinton has urged newspaper editors to focus more attention on the depletion of the world's oil reserves. In a June 17 speech to the Association of Alternative Newsweeklies convention in Little Rock, Arkansas, Clinton said a "significant number of petroleum geologists" have warned that the world could be nearing the peak in oil production. Clinton suggested that at current consumption rates (now more than 30 billion barrels per year, according to the International Energy Agency), the world could be out of "recoverable oil" in 35 to 50 years, elevating the risk of "And then finally, and I think most important of all, more important than the deficit, more important then healthcare, more important than anything, is we have got to do something about our energy strategy because if we permit the climate to continue to warm at an unsustainable rate, and if we keep on doing what we're doing 'til we're out of oil and we haven't made the transition, then it's inconceivable to me that our children and grandchildren will be able to maintain the American way of life and that the world won't be much fuller of resource-based wars of all kinds.”

Source: Made in Japan (1986), p. 164.

We are a sovereign state, not a nation-state. Unlike, say, Denmark, we have no official language and no state religion. Our identity is oriented toward the future, not the past. We do have birthright citizenship — though that, curiously, is something many of today’s national conservatives want to abolish. Our national borders have changed repeatedly and may change again.</p><p>America is the country under whose banner the descendants of slaves give military orders to the descendants of slave owners and stand guard alongside the children of immigrants from Greece and Mexico in places like Panmunjom. It’s where the biological son of a Syrian immigrant created our first trillion-dollar company. It’s where Jews celebrate Christmas by going out for Chinese food.</p><p>All this is the essence of America’s exceptionalism. It does not require open borders, rule by U.N. mandarins, obeisance to progressive pieties or any of the other ostensible predations of “globalism” that conservative nationalism claims to oppose.</p>
The New Conservative Pyrite (2019)