Political experts were quick and unanimous Monday in forecasting a tough road ahead for the Democratic Party of Japan, expressing concern that its Upper House election loss will threaten Prime Minister Naoto Kan on all fronts.

"No opposition party is going to join this government," Columbia University professor Gerard Curtis said, predicting Kan will have a hard time finding a coalition partner to secure a majority in the Upper House.

Speaking in Tokyo at the Foreign Correspondents' Club of Japan, Curtis said the DPJ may have had a better shot at joining hands with others if it had won at least a few more seats.