As Japan kicks off 2018, Prime Minister Shinzo Abe faces what is perhaps the biggest political dilemma of his career: whether to call the nation's first-ever referendum on revising the postwar Constitution.

Abe sees rewriting the U.S.-drafted charter, which has remained untouched since its inception 70 years ago, as his legacy project — so much so that, frustrated by long-stalled progress, he got the ball rolling last year by making a surprise announcement that he wants to see the supreme law revised by 2020.

"This year is going to be a year of action. We will put into action, step by step, policy goals that we promised in last year's general election" Abe said in a New Year's statement released Monday. Constitutional revision was among the key pledges his ruling Liberal Democratic Party made ahead of the Lower House poll.