TOKYO (BLOOMBERG) - With Japan's opposition wracked by infighting, any challenge to Prime Minister Shinzo Abe's grip on power- as his popularity slides after a series of scandals and missteps - is likely to come from his own party.
Most lawmakers from the ruling Liberal Democratic Party (LDP) are members of factions, in a system that dates back to the party's founding in 1955, when two conservative groups merged. The combined entity has gone on to dominate Japanese politics, in power for all but a handful of years over the past six decades.
Over time, the factions have splintered, merged and changed direction, nowadays loosely solidified around personalities or policy preferences. While about a fifth of the lawmakers are independent, horse-trading among factions can be a decisive factor in picking prime ministers.
The next LDP leadership election is expected in September 2018 and, assuming the party stays in power, the winner will be prime minister. Mr Abe can call a general election at any time until December of next year.
Since candidates need 20 backers to run for the LDP's top job, lawmakers without a clear faction - like Internal Affairs Minister Seiko Noda, and Mr Shinjiro Koizumi, the son of a former prime minister - are disadvantaged though they are popular with the public.
Contenders need a majority of votes from Parliament and regional assembly members to win.
Here are the main factions among the 409 LDP lawmakers in Parliament:
1. Abe-Hosoda (95 lawmakers)
Mr Abe is part of the largest faction, a conservative group founded in 1979 on principles of good governance. The faction also produced his mentor Junichiro Koizumi, who served as prime minister for more than five years.
Its image has been damaged by scandals involving ministerial members the past few months, and the group lost two Cabinet positions in a recent reshuffle. The group's leader is officially ex-chief cabinet secretary Hiroyuki Hosoda.
2. Aso (59 lawmakers)
Deputy Prime Minister and Finance Minister Taro Aso controls the second-biggest faction. A former prime minister, who has served under Mr Abe since 2012, Mr Aso has pledged to keep supporting the Premier and his fight against deflation.
Still, analysts say the 76-year-old will probably seek a role as kingmaker in the next leadership vote and may yet want another stint in the top job.
3. Nukaga (55 lawmakers)
Former finance minister Fukushiro Nukaga's faction dominated the LDP in the late 1980s and early 1990s, but its strength has since faded. It has two ministers in the Cabinet.
4. Kishida (46 lawmakers)
Mr Fumio Kishida, who was lauded by Mr Abe in August as a future leader, heads the party's oldest faction, which was formed in 1957.
Mr Kishida's group fared the best in Mr Abe's recent Cabinet reshuffle: It now has four ministers, more than any other faction.
Mr Kishida himself left the Cabinet to take a party role, putting him in position to challenge Mr Abe next year.
The group is relatively dovish on defence and Mr Kishida has said he sees no need to change the pacifist Article 9 of the Constitution, a policy favoured by Mr Abe.
5. Nikai (44 lawmakers)
Headed by LDP Secretary-General Toshihiro Nikai, the fifth-largest faction was founded in 1999. Once a home for the party's right wing, its image has changed considerably under Mr Nikai.
It is now known for Mr Nikai's friendly ties with China, with whom Mr Abe has had periodic bouts of tension over disputed territory.
6. Ishiba (19 members)
Two years ago, former defence minister Shigeru Ishiba founded his own group, seen as a bid to bolster his chances of becoming party leader. It has 19 members and one Cabinet minister.
Mr Ishiba topped Mr Abe in a recent survey asking voters who should lead the LDP next year, and he is expected to throw his hat in the ring. Mr Ishiba has expressed concern about rushing to change the Constitution and urged the government to maintain its target of reaching a primary balance surplus by 2020.
7. Independents/Others (91 members)
A number of smaller groups and informal alliances exist among other lawmakers. One of these is led by former LDP leader Sadakazu Tanigaki, who has been out of the public eye since injuring his spine in a bicycle accident a year ago, but is reported to be planning a comeback. While none of the groups is overly strong, their votes may be crucial in a close leadership race.