By one hopeful theory, Nader was playing a game of chicken. He was trying to pressure Gore to move to the left. Then he would drop out of the race. Does the 'game of chicken' means 'game of threatening'?
"Chicken" is often used as a slang term to denote cowardice or lack of resolution. Someone thinking of bungee jumping but changing their mind at the last moment might be said to have "chickened out" of jumping.
"Playing chicken" is a somewhat foolhardy pursuit where two people put themselves in a dangerous situation where one has to lose their nerve and take evasive action, and the winner is the one who holds their nerve longest. The classic example is two people driving their cars directly at each other, with the obvious threat of a head-on collision. In most cases, one person's resolution breaks first and they swerve to one side, but cases have been recorded where the game was a draw, even if the "winners" were no longer alive to celebrate, proving just how deep is the well of potential human stupidity.
In this case, the term "game of chicken" is referring to the political dangers rather than the physical ones, but Nader and Gore seem to have maneouvred themselves into just such a stand-off situation, and everyone was interested as to whose nerve would hold longest.