While it is certainly true that Ishiba has the experience in the defence portfolio, and has been a long-time advocate for collective self-defence (as revealed in his 2011 book Kokubō, or ‘National Defence’), for a potential future prime minister to acquiesce to PM Abe’s wish and take a cabinet post would be unusual, to say the least. Readers would remember that Ishiba stood against Abe during the LDP party leader election in September 2012, where he was given the Secretary General role as a sort of consolation prize after being narrowly defeated by Abe’s factional supporters. Since 2012 Ishiba has kept a comparatively low profile, only emerging periodically to comment on party and other matters (including his infamous suggestion that those opposed to Japan`s new security privacy laws were themselves terrorists) (J). Members of his non-factional support group have pointed out (J) that should Ishiba accept a cabinet post, he would effectively lose his voice and would be forced to tow Abe’s line on security matters, thereby lessening his own influence over the defence debate (and ultimately influencing his political fortunes).
While the offer is tempting, Ishiba would know that to accept it would mean stifling his ambitions yet again for the sake of Abe. If Ishiba refuses the position, he might end up with no portfolio at all, reduced to a mere party member. But that would be a particularly damaging route for PM Abe to take, given that support within the LDP for Ishiba is high among regional LDP members and they would not look kindly upon a PM seeking to silence such a prominent member of the LDP. Ishiba himself has said that he would accept any position should it be offered to him, but that seems more like an attempt to force Abe to reveal his intentions early, and Abe won`t fall for it.