TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe is facing his biggest political crisis since taking office more than five years ago, as suspicions swirl about a land sale to a school operator with ties to his wife.

Japan's Prime Minister Shinzo Abe atttends a parliament session at the Upper House in Tokyo, Japan March 19, 2018. REUTERS/Issei Kato

Abe has denied that he or his wife, Akie, intervened in the heavily discounted sale of state-owned land to the school operator, Moritomo Gakuen, or that he sought to alter documents related to the deal.

Finance Minister Taro Aso, a close Abe ally, has also denied involvement in alterations officials in his ministry made to the documents.

But a spate of weekend opinion polls showed support for Abe’s cabinet sinking as low as 31 percent, with majorities saying he bears some responsibility.

The sagging support could dash his hopes of winning a third three-year term as leader of the governing Liberal Democratic Party (LDP) in a September party election. A victory would put him on track to become Japan’s longest-serving premier.

Below are possible scenarios for Abe’s political future.

ABE’S RATINGS RECOVER, HE WINS THIRD TERM

Last year, Abe, 63, also saw his ratings plummet over the Moritomo land deal and other matters. The LDP suffered a historic trouncing in a Tokyo assembly election.

But he recovered in the polls, and his LDP-led coalition won a two-thirds “super majority” in a snap lower house election in October, helped by fragmentation of the opposition parties, low turnout and his stern stance toward North Korea’s nuclear and missile threats.

That could happen again, especially if there are no further big revelations in the Moritomo affair, no fresh scandals appear and Abe demonstrates skill on the diplomatic front.

Abe could decide to sacrifice Aso - who has said he has no intention of resigning - but that could backfire by focusing criticism even more firmly on the prime minister and depriving him of a “breakwater” against public ire.

If his ratings recover and his backers in the LDP hold firm, Abe could win a third term as party leader and stay in office into 2021.

ABE RESIGNS BEFORE SEPTEMBER

If Abe’s ratings fall further and stay low, he may decide to step down before the September vote, although having quit once, he is probably reluctant to do so again. Abe abruptly resigned in 2007 after a year in office plagued by scandals in his cabinet, a deadlocked parliament and poor health.

If he steps down, Abe may try to throw his support behind former foreign minister Fumio Kishida, 60, to succeed him with backing from other party heavyweights. Kishida now serves as LDP policy chief.

The LDP would have to hold a special leadership vote, but could just poll members of parliament rather than including rank-and-file members. That would give Kishida, a low-key lawmaker seen as less hawkish than Abe, an edge over former defense minister Shigeru Ishiba, who is popular with the party as a whole but less so among lawmakers.

Both Kishida and Ishiba have expressed concerns about Japan’s bulging public debt.

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ABE LIMPS TO SEPTEMBER

A weakened Abe could last until September, when he could step aside or run again and face a potentially fierce face-off with Ishiba.

If other rivals also throw their hats in the ring, the anti-Abe vote could be divided enough for him to eke out a victory. But if that happened, he could have trouble pushing his controversial agenda of revising the pacifist, post-war constitution and deregulating the labor market.

The election would include votes by both members of parliament and the rank-and-file, which could give Ishiba, 61, an advantage.

Internal Affairs Minister Seiko Noda, 57, has also expressed a desire to run, but is thought to have little chance of winning.