ANY President of the United States who takes office believing that he
will be able to treat foreign affairs as a minor part of his job is
tempting fate. For Bill Clinton the temptation has been especially
perilous. Unlike his eight immediate predecessors, Mr Clinton became
president at a time when the simplifying rigors of the cold war had
evaporated. This removed the only conceivable threat to America's
existence, but at the cost of depriving the United States of a clear
idea of its role in the world just when--as the sole superpower--its
ability to perform that role became more important than ever.
The result for Mr Clinton has been a series of muddles, zigzags,
fiascos and falling opinion-poll ratings. etc.
**
rigor (Merriam-Webster):
a condition that makes life difficult, challenging, or uncomfortable
especially : extremity of cold
the rigors of a New England winter
strict precision : exactness. logical rigor.
Tentatively one might suggest that what characterizes science is the rigor of its methodology …
I think it refers obliquely to the cold of winter, and also makes reference to the rigidity of cold war relations.
Edit:
During the cold war, things were black and white. Simple. The Soviets were the bad guys. The US and its allies were the good guys. (From a US president's point of view.) This schematic could be used (in those days) to simplify complex international relationships.