Climate change is, as Barroso put it, "the defining challenge of our time", while struggling economies are the defining challenge of today.
Mr Monti faces his defining challenge.
"Africa is poised for a defining challenge," he said.
"This is a defining challenge of our future," he said.
Calculating the value of these relationships has become a defining challenge for businesses and individuals.
Climate change, and our success or failure in dealing with it, will be a defining challenge.
"They see this, very much as I do, as the defining challenge of their lives".
These kinds of digital, ethical problems represent a defining challenge of the 21st century.
"Iraq is the centerpiece of the defining challenge of our time".
And, with President Obama recently declaring inequality the "defining challenge of our time", Reich's policy critique is especially apposite.
But for many Americans, what Mario Cuomo called "the struggle to live with dignity" remains our defining challenge.
