Last week the U.S. House voted overwhelmingly in favor of an anti-Russia resolution so full of war propaganda that it rivals the rhetoric from chilliest era of the Cold War.
The noun era is a singular count noun, moreover, it's modified by the phrase of the Cold War and has a superlative adjective attached: the chilliest era. Is it possible to drop an article in this case?
There are instances when we can omit the definite article (and the indefinite) before a superlative adjective (like highest, bravest, most efficient etc.).
- The smartest boy in our class solved the problem.
- We have a lot of smart boys in our class. John is smartest (of all).
In sentence 1, the superlative adjective "smartest" is attached to the noun "boy". It serves as an attribute of the noun boy, and is called an attributive adjective.
Note that the key verb in the sentence, solved, connects to the noun boy.
In sentence 2, the superlative adjective "smartest" is not attributive: it does not connect to a noun directly, although we can add "of all" at the end of the sentence.
Also note that it connects directly to the key verb of the sentence, is. We can even change the word order:
Smartest among our classmates was John.
Such adjectives are called predicative: they are part of the predicate.
But in your example, the chilliest describes the noun phrase era of the Cold War and is clearly an attributive adjective, so the is necessary.
We can try to make it non-attributive:
Chilliest of the Cold War eras was the era during which the US rhetoric was comparable to the war propaganda overfilling the anti-Russian resolution overwhelmingly voted in favor of by the U.S. House last week.
Now, the superlative adjective chilliest connects to the verb was and the use of the article is optional. Only we had to put the whole sentence upon its head.
Reference: Quirk et al., A Comprehensive Grammar of the English Language, Topic 7.84, "Article usage with comparatives and superlatives".