It is widely viewed that Prime Minister Shinzo Abe will be re-elected as president of his ruling Liberal Democratic Party in its leadership race in September 2018, grabbing a chance to become Japan's longest-serving leader.

But a possible failure in the process of pursing his long-cherished goal of achieving the first-ever amendment to Japan's pacifist Constitution could deal a blow to Abe and weaken his re-election prospects in the year, seen as otherwise eventless in Japanese politics, political experts say.

In 2017, the 63-year-old prime minister saw his approval ratings plunge at one point in early summer due to favoritism allegations leveled at him, but then consolidated power after the LDP won a landslide victory in the lower house election in October.

In a historic move, Abe's administration enacted a law enabling Emperor Akihito, 84, to abdicate, making him the first living emperor to retire in around two centuries.

In diplomacy and security, Abe succeeded in forging close ties with U.S. President Donald Trump, who took office in January, and earned a reputation to some extent due to his hard-line stance on North Korea, which continues with its nuclear and missile development.

Without any national elections scheduled in 2018, all eyes will be on the LDP's leadership contest in the autumn.

Former Foreign Minister Fumio Kishida has been viewed as a leading candidate to be Abe's successor. It has even been rumored that a "peaceful transfer of power" would take place from Abe to Kishida.

But the 60-year-old LDP policy chief remains low-key despite his more than four-year tenure in the key ministerial post, during which he was involved in realizing former U.S. President Barack Obama's historic Hiroshima visit.

Hitoshi Komiya, an associate professor of contemporary Japanese history at Aoyama Gakuin University, took a negative stance on Kishida's appointment as party head, given that an upper house election is scheduled in July 2019. "Lawmakers tend to prefer a leader who can appeal to voters to win the election," he said.

Internal Affairs and Communications Minister Seiko Noda, 57, and former LDP Secretary General Shigeru Ishiba, 60, make no secret of their desire to throw their hats into the ring. But it is unclear whether they could muster the support of 20 party lawmakers required to run in the race since Noda does not belong to any intraparty group and Ishiba's faction is a small one.

Meanwhile, Foreign Minister Taro Kono has recently seen a spike in his popularity after assuming the post in early August in a Cabinet reshuffle aimed at reviving support for Abe.

In contrast to Kishida, Kono's outspoken style draws public attention, pushing him to be a likely candidate. Kono, a 54-year-old graduate of Georgetown University in Washington, speaks fluent English in the international arena.

But whether he could become a rival to Abe all depends on the decision of Deputy Prime Minister Taro Aso, who, as the party's heavyweight, doubles as finance minster and is also the head of a faction to which Kono belongs, according to Komiya.

Although some of them are likely to compete with Abe in the upcoming contest, a lack of strong contenders would raise the premier's chances for winning another three-year term to become the longest-serving prime minister, surpassing Taro Katsura, who served in the post for 2,886 days in the early 20th century.

After his first term as prime minister between 2006 and 2007, Abe returned to power in late 2012.

In a speech on Dec. 19 in Tokyo, Abe reiterated his wish for accelerating discussions over constitutional revision, saying, "We have to deepen debate over the Constitution and discuss well how the nation should be shaped and exist."

Originally, constitutional amendment was a key objective of Abe's grandfather and former Prime Minister Nobusuke Kishi, and also a stated goal of the LDP, which believes Japan should have its "own" Constitution instead of the current text drafted during the U.S.-led occupation of the country after World War II.

In May, Abe said he wants the revision to take effect by 2020 and proposed an idea to change its Article 9 by adding an explicit reference to the Self-Defense Forces, citing the need to end arguments by some constitutional scholars that an organization even for self-defense violates the war-renouncing charter.

Unlike in 2018, there will be plenty of political events in 2019, including unified local elections in April, the emperor's abdication at the end of the month and the upper house election in July. Against that backdrop, calls are growing within the LDP for pushing ahead with the constitutional revision procedure in a relatively calm 2018.

But the bar is not low to realize the move. After deliberations by the Commissions on the Constitution of the upper and lower houses in the Diet, amendment proposals need to be given approval from two-thirds of lawmakers in both chambers. Then, the proposals must be approved by a majority of voters in a national referendum.

The LDP is seeking to present its amendment proposals to the constitutional commissions during the ordinary Diet session to be convened on Jan. 22. Whether they would be approved during the 150-day session will be the biggest challenge for Abe.

The prime minister is believed to have a golden opportunity to push for his political agenda, as the ruling bloc and other pro-amendment forces have secured two-thirds of the seats in each of the two parliament chambers.

But in late December, the LDP summarized its discussions on constitutional amendments in an interim report, citing two ways in revising the war-renouncing article -- one advocated by Abe to simply add a reference to the SDF and another to delete the article's second paragraph that renounces the right to maintain military forces and other war potential.

Political commentator Norio Toyoshima pointed out the fact that the interim report containing two options over the most contentious issue means the LDP is struggling to unite opinions within the party.

The commentator said he had expected the LDP may have difficulty in negotiating with its coalition partner Komeito party, as the party describes itself as a champion of peace and has been reluctant to revise Article 9. But he said the LDP tumbled at the "entrance" of the procedure for amending the Constitution.

If Abe stalls the procedure before it gets to a national referendum, possibly before the president race, it is inevitable that he would lose his grip on power. "That will be the best chance for those aiming to topple Mr. Abe," Toyoshima added.