The administration of Prime Minister Junichiro Koizumi may have heard the first whack at the final nail in its coffin.
A woman who claims she was a longtime lover of Koizumi's right-hand man went public Tuesday.
Kanako Yamada, a former hostess who says she was the lover of Taku Yamasaki, secretary general of the Liberal Democratic Party, spoke at the Foreign Correspondents' Club of Japan about her nearly 10-year relationship with the party's second-ranked figure.
Yamada, who first appeared in a weekly magazine under a fictitious name about a year ago, has come out and published a book on the alleged affair, saying that Yamasaki has been "insincere" in denying their relationship and that he does not treat women like humans.
Yamasaki has categorically denied the allegations, and has filed a libel lawsuit against her and the weekly Shukan Bunshun, which carried a series of articles giving Yamada's account.
At a regularly scheduled news conference earlier the day, Yamasaki declined to comment on Yamada's scheduled media appearance, saying the lawsuit is already under way.
"As I have said before, this is a private matter and I have filed a lawsuit," he said.
But despite Yamasaki's denial, political sources said the sex scandal has already had a serious impact on voters particularly women in his home district, the Fukuoka No. 2 constituency.
"A view is now spreading that Yamasaki will have to fight a severe uphill battle in the next election," political commentator Minoru Morita said. "He may even not be re-elected."
Morita added he cannot remember any past LDP secretary general that has faced such grim prospects in an election.
Among the leaders of the LDP's factions, Yamasaki is seen as the only one staunchly behind the prime minister.