The DPJ’s two FPP lower house seats are held by Kantoku Teruya in the Okinawa Prefecture 2nd District and Yasumasa Shigeno in the Oita Prefecture 2nd District. Of the two, Teruya’s seat is more likely to remain with the DPJ if it leaves the coalition. Shigeno’s situation is harder to read, but it’s not clear that the SDP will be better off here if it remains in the coalition.
Teruya was first elected as an anti-military independent to national office in 1995 to the upper house for the single seat that was up for election that year in two-seat Okinawa. He yielded his position as the anti-military candidate in the 2004 upper house election to Keiko Itokazu (who easily defeated the LDP candidate), but returned to the Diet as the lower house member from the Okinawa Prefecture 2nd District as a member of the SDP. He was reelected in 2005—when the DPJ candidate finished a near-fringe candidate third behind the LDP also-ran—and 2009. Through all this, he has also enjoyed the support of the Okinawa Social Mass Party, which has drifted to the left over the years as it lost a good portion of its support base to the LDP and DPJ. My guess is that he will be more helped than harmed by a DPJ challenger, who would only wind up as a spoilsport for the LDP candidate by splitting the pro-military vote. On the other hand, if the DPJ remains in the coalition, Teruya may bolt the SDP and run as an independent in the next lower house election, which would be the surest way for the DPJ to lose that seat.
Shigeno’s situation is different. A dyed-in-the-wool SDP member who worked his way up the prefectural civil service labor union ladder, then turned to politics fulltime, serving as a prefectural assemblyman for 26 years, and winning a national office in the 2000 lower house election as a regional proportional candidate. (He ran simultaneously in the Oita Prefecture 2nd District, where he lost to Seishiro Eto, the LDP incumbent.) His subsequent track record: (2003) FPP loss, regional loss; (2005) FPP loss, regional win; (2009) FPP win—finally beating Eto in a close race. Shigeno had been gaining votes in each election even before the historical alliance in the 2009 election, so it’s not a given that he will lose his FPP seat—possibly against a rookie if Eto, 72 by the time a 2013 election rolls around—if he DPJ withdraws its support, in which case, he will still have an excellent chance of making it back on the SDP’s regional proportional ticket. On the other hand, he is not a shoo-in even if the SDP stays in the coalition, given that Eto managed to run a close second in an election that turned out to be a disaster for the LDP overall.
To sum it up, if the SDP remains in the coalition, it may lose the Okinawa FPP seat through defection while the Oita FPP seat is not a sure thing even with DPJ support. If the SDP leaves the coalition, it is highly likely to retain the Okinawa FPP seat while there is a good chance that it will lose the Oita FPP seat.
The SDP is not, or course, a single-issue party, and many things can happen between now and whenever. But the impact of a withdrawal from the coalition on the SDP’s FPP seats is ambiguous at worst. Given the predictable, immediate fallout on the upper house proportional ballot and its reputation as a party of principle/protest as well as the institutional memory of the disaster that the 1994-1995 cohabitation under Tomiichi Murayama turned out to be, I have to put my money on a formal split.
And I’ll know soon enough if I’m wrong.
Addendum (blooper alert): Anonymous reminds me in the comments that Kiyomi Tsujimoto made it through in the Osaka 10th District. Thanks. That also provides a good motive for Tsujimoto’s reluctance to speak out against Hatoyama after Fukushima resigned. The SDP will most likely have to kiss her seat goodbye if the DPJ decides to field its own candidate there, meaning that she would have to take up the 1 seat that the DPJ will win in the 29-seat Kinki region proportional district. Add this long-term outlook to the threat of a second DPJ upper house candidate in the Niigata Prefectural District and a collaborative relationship on an issue-by-issue basis becomes attractive from a purely electoral point of view. After all, the SDP should be able to maintain its 2 upper house proportional seats even if its share of the national vote falls to 3%. Whether the SDP activists will accept this line of reasoning—if indeed the SDP leadership iss thinking along these lines—is another matter altogether. And that’s about as far as my arithmetic takes me.
* In fact, some DPJ political operatives are reportedly threatening to field a second candidate for the two Niigata Prefecture upper house seats coming up for the 2007 election. The SDP and the DPJ currently hold one seat each. Ichiro Ozawa is pushing a second candidate in all the other two-seaters but has refrained from doing so as a favor to the SDP.