Prime Minister Shinzo Abe said Sunday he will run in the Liberal Democratic Party’s leadership election next month, setting the stage for a two-way race against former Defense Minister Shigeru Ishiba.

“For three more years, I am determined to lead the nation as LDP president and prime minister,” Abe told reporters in Tarumizu, Kagoshima Prefecture. “I will take the initiative in creating the nation in the period beyond the Heisei Era.”

With official campaigning scheduled to kick off on Sept. 7, the ruling party will hold the election, which will effectively decide the next prime minister, on Sept. 20.

Noting that his LDP won last October’s House of Representatives election by a landslide, Abe claimed, “It is my responsibility to live up to the public mandate.”

Ishiba welcomed Abe’s official announcement, saying “It is the LDP’s responsibility to offer the nation and the public as many opportunities as possible to hear debates (among LDP presidential candidates).”

LDP policy chief Fumio Kishida, who has decided not run this time, said Sunday at a party meeting in Gunma Prefecture he will throw his hat into the ring when the LDP holds its next presidential election, likely to be in three years time.

Abe is predicted to win because five of the LDP’s seven intraparty factions, which encompass around 70 percent of its members, have said they are ready to back him.

Victory would give Abe another three-year term, putting him on track to become Japan’s longest-serving prime minister.

In the election, the contenders will try to secure a majority of the 405 votes cast by the party’s Diet members and the same number of votes cast by rank-and-file members. If no one wins a majority in the first stage, a runoff will be held that gives more weight to the Diet members’ ballots.

Ishiba, 61, who has held such key such as secretary-general and minister in charge of regional revitalization under Abe, is trying to broaden his support base among the party’s rank-and-file.

The LDP president is trying to boost his popularity outside big cities as the ballots cast by both the Diet members and rank-and-file members will have equal weight in the first round.

In an apparent attempt to demonstrate his emphasis on rural areas outside Tokyo, Abe, 63, chose Tarumizu as the place to officially declare his candidacy.

Now that Abe has officially thrown his hat into the ring, debates are set to start on issues including whether to amend the Constitution, how to boost regional economies and Abe’s handling of the government over the past five years and eight months.

Abe, who was re-elected unopposed in 2015, was defeated by Ishiba in the initial stage of the previous election in 2012 but managed to come from behind in the runoff.

The two veterans are expected to officially register their candidacies on Sept. 7, setting off the campaign period.

One focus of the debate is likely to the men’s plans for war-renouncing Article 9.

Abe has called for adding an “explicit reference” to the Self-Defense Forces to ensure there is no way for them to be deemed “unconstitutional,” and said the LDP should submit constitutional revision proposals to the extraordinary Diet session expected to be convened in the fall.

But Ishiba has insisted amendments to Article 9 are not a priority, especially given the public’s lack of understanding on the issue.

He instead said it was urgent to revise the Constitution to give the prime minister extraordinary powers to deal with emergencies including natural disasters.

On the economic front, Abe is expected to play up the results of Abenomics, his economic growth package centered on fiscal spending, radical monetary easing and vows of structural reform.

At a news conference Friday, Ishiba announced pledges aimed at boosting regional economies, including by transferring ministries, agencies and large companies to areas outside of big cities.