By Linda Sieg
TOKYO (Reuters) - Prime Minister Shinzo Abe became Japan's longest-serving premier on Wednesday, a remarkable feat for a leader who once quit in humiliation, but the day was marred by questions about possible election law violations and worries about the economy.
Abe, 65, who served his first term for just one year before quitting in 2007, made a comeback in December 2012, promising a stronger military and a revamped economy while aiming to revise Japan's post-war, pacifist constitution.
Pointing to such challenges as Japan's ageing population and constitutional revision - a divisive topic - Abe vowed to push ahead in the last two years of his term as Liberal Democratic Party (LDP) leader, which ends in September 2021.
"I want to tackle policy issues with my heart and soul, with a sense of treading on thin ice and staying on my toes, not forgetting the spirit with which I began," Abe told reporters.
Abe has won relatively high marks for his diplomacy. His warm ties with U.S. President Donald Trump may have averted worst-case scenarios in trade feuds, although scant progress has been made on a territorial row with Russia and relations with South Korea are frigid.
Wednesday marked Abe's 2,887th day in office over his two stints as prime minister. That broke the record set by Taro Katsura more than a century ago.
Abe has led his ruling coalition to six national election victories since returning, surviving allegations of cronyism and scandals over falsified data by bureaucrats.
Those victories were aided by a fragmented opposition and unpleasant memories of the rocky 2009-2012 rule by the novice Democratic Party of Japan.
But since a cabinet reshuffle in September, two ministers - both close allies of Abe - have resigned over allegations of election campaign law violations.
Now Abe is under fire over accusations he not only favored supporters with invites to a state-funded cherry blossom viewing party but may have broken campaign laws by subsidizing backers' attendance at a reception the night before.
Abe has denied wrongdoing. On Wednesday, he said that it was up to the public to assess his accountability but that he would answer more questions in parliament.
A Nov. 16-17 Asahi newspaper poll showed 68% weren't convinced by his explanations, though support was steady at 44%.
Concerns the economy is headed for recession also cloud Abe's future. Japan's exports tumbled at their quickest pace in three years in October amid weakening demand from the United States and China.
(Reporting by Linda Sieg. Editing by Gerry Doyle)