The Liberal Democratic Party candidate's victory in the Lower House by-election in the Hokkaido No. 5 constituency on Sunday may embolden Prime Minister Shinzo Abe's ruling coalition ahead of the Upper House race this summer. The close race in the first Diet election since the 2014 general election of the Lower House should also remind the opposition camp that campaign cooperation will be the only viable way to compete with Abe's dominant ruling bloc. The Democratic Party and the Japanese Communist Party will need to quickly review Sunday's outcome and rebuild their strategy for the Upper House election.

The Hokkaido by-election to fill the vacancy left by the death of LDP veteran and former Lower House Speaker Nobutaka Machimura last year was seen as a test of voter sentiments ahead of the triennial Upper House race, which will likely be held in July. As the LDP was unable to field a candidate in the Kyoto by-election also held Sunday after its member resigned over an extramarital affair, a defeat in the Hokkaido race could have dealt a severe blow to the Abe administration.

It was the first major electoral test for the Democratic Party after its merger with Ishin no To (Japan Innovation Party) last month, and the race also served as a test case for the campaign cooperation that opposition parties are pursuing for the Upper House election to challenge Abe's ruling alliance. The JCP withdrew its candidate earlier this year to throw its support behind an independent also backed by the Democratic Party and two other opposition forces.