Poll loss another nail in Koizumi's coffin.

Prior to the crushing defeat of the ruling camp in Sunday's House of Councillors by-election in Niigata Prefecture, all Diet elections since the start of the administration of Prime Minister Junichiro Koizumi in April last year had resulted in Liberal Democratic Party victories, mainly on the strength of Koizumi's high popularity ratings.

Koizumi successfully led the LDP to triumph in the upper house elections in July, three months after taking power.

Koizumi also was credited for wins by LDP candidates in two subsequent Diet elections: a House of Representatives by-election in Miyagi Prefecture Constituency No. 4 and a lower house by-election in Shiga Prefecture's Constituency No. 2, both in October. …