Beer Sheva, Israel (CNN) Israel is voting in an election on Tuesday that's gearing up to be as defining for the country as it is challenging for its prime minister.

Benjamin Netanyahu -- who was the country's youngest prime minister when he was elected in 1996, and now hopes to become its longest serving -- faces his toughest electoral challenge in 10 years.

It comes in the shape of Benny Gantz, a former Chief of the General Staff of the Israel Defense Forces, who has gathered together a "blue and white" alliance, named after the colors of the Israeli flag.

By its very nature -- a collection of centrist and center-right political parties that includes no fewer than three former IDF chiefs of staff -- the alliance presents a substantial challenge to the man who has dominated and reshaped Israeli politics for the past decade.

Having three military heavyweights lined up against him makes it harder for Netanyahu to play the security card that has served him so well for so long.

Read More