Define Gauntlet in "the gauntlet of..."

Solution 1:

Two separate words, although they're spelled and pronounced the same. The first "gauntlet" comes to us through the French for glove, and it refers to hand armor. Go here for pictures. Tossing one's glove before an opponent was a challenge to fight, thus the idiom meaning to challenge. The second "gauntlet" was originally "gantlope," which comes from the Swedish gatlopp, literally "gate passage" and refers to a punishment of forcing someone to run between two lines of people who struck the unfortunate runner. Thus the word's use as a trial or ordeal. The OED suggests that the word entered English during the Thirty Years War and lost its pronunciation to the first gauntlet.

To makes things worse, there's also the word "gantlet," which is the configuration of two railroad lines that have to share a narrow passage. Go here for a diagram and here for a picture.

Solution 2:

The reference is to running the gauntlet, originally a form of punishment where the individual was made to run between two rows of soldiers who would punch and beat him as he ran, but now more often taken to refer to a stressful and reasonably protracted period of tests or exercises.