The mood was grim Sunday at The New Otani Hotel, the Democratic Party of Japan's election base in Tokyo, as the reality set in that the ruling coalition had lost its majority in the Upper House.

In one of the hotel's large halls, nearly 400 seats had been prepared for domestic and international reporters, and dozens of TV cameras were lined up by the back wall. But the gathering clearly lacked the excitement that surrounded the party's historic general election win last summer, as gloomy DPJ executives took turns answering reporters' questions.

"I believe there are many contributing factors" to the DPJ's poor performance, said DPJ Deputy Secretary General Goshi Hosono, adding that Prime Minister Naoto Kan's proposal to open debate on a potential consumption tax hike may have proved the most damaging.