Aiya, think again.
Whether is TCB, TJS or KFC being the President, the consitution is still that President must act under the PM's advice.
So there is little difference of who being the President other than the Psyological one.
Now, if TJS never entered the fray, the 25% is likely to vote for Tan Kin Lian who is at least more neutral / against PAP then Tan Cheng Bock.
No doubt TCB is good, but his influence is limited to the West, just like CST in Potong Pasir and LTK in Hougang.
The whole nation knows the existence of 3, but only in areas surrounding above mentioned will support these 3 people respectively and this is y LTK concentrate his battle in the East.
And the fact is, more opposition voters vote Tan Jee Say, and about half of the PAP voters vote for Tony Tan.
Hence, it should be that had CST did not endrose TCB, the president might have been TJS instead for the near 10% swing vote.