Official campaigning for the July 21 Upper House election kicked off Thursday in what could be a make-or-break vote for Prime Minister Shinzo Abe's career-long ambition to revise the post-war Constitution while also serving as a litmus test for his economic policies, including the planned consumption tax hike in October.

The biggest focus will be on whether the Liberal Democratic Party and other forces in favor of constitutional amendment will be able to retain their current two-thirds supermajority — a key threshold needed to initiate a national referendum on the divisive topic.

But at the same time, political observers say the outcome of the election may not provide a clear-cut clue as to whether Abe's quest for constitutional revision will become a reality. A persistent resistance by coalition partner Komeito to revise war-renouncing Article 9, not to mention the ever-divergent attitudes among opposition forces, blur the line between pro- and anti-revision forces, leaving some room for ambiguity, observers say.