For both PP and HG there have been nibbles around the corners as with CCC and BG. The point I believe is that when any opposition candidate gets in as far as I know on recent history the gerrymandering has been of a limited four five blocks here, four five blocks scenario. The question as always is does that limited nibbling serve as an excuse for one's loss or the PAP's dangling of carrots in view of the carrots thrown at HG and PP voters for the last twenty years or is the reason more substantive that those who got in and lost were unable to sustain their initial political momentum.
Chiam won Potong Pasir in GE84, GE88 and in GE91, he won by a large majority of 69.64%. To be exact, he won by 7,096 votes more. So any contest in Potong Pasir would be quite immuned to small scale gerrymandering. In GE97, when the HDB upgrading was first used by PAP to win support, Chiam popularity dropped to 55.14%. In that GE, Chiam won by 1,814 votes more. Many in Potong Pasir hoped to have upgrading and so this affected Chiam's share of votes.
LTK won Hougang in GE91 by a difference of 1,134 votes but he was a teochiew and was very popular with the teochiew folks there. LTK was praise by LKY on his performance in Parliament and his performance was used to contrast with that of Ling and Cheo, which LKY described as dismayed. All these news were widely carried in the media. LTK has also been hardworking in serving his residents too. In GE97, LTK won by a larger majority of 58.02%. There was less clamouring for upgrading in Hougang and so the HDB upgrading carrot was less effective there. He won by 3,722 votes more.
A bit of background on events surrounding SDP.
Between 1991 and 1997, Chee and SDP were relentlessly hounded by the press.
One particular case: The SDP healthcare report was thoroughly discredited by PAP and Select Parliamentary Committee was convened to look into one typo error. As a result, Chee and his CEC members were fine heftily and their credibility were shattered.
Ling won Bukit Gombak in GE91 by only 654 votes more or 51.4% of total votes. In GE97, there was a three cornered fight as Chiam broke his promise and sent a candidate under SPP to contest Gombak. The infighting between Chiam and SDP's leadership carried into the GE97 and this created a very bad perceptions of SDP as a political party in voters mind. As a result, Ling only managed to get 28.42% of the total votes.
Cheo won Nee Soon Central in GE91 with a very slim majority of 168 votes. Some shifting of a few blocks here and there would have meant Cheo had no chance of winning. In GE97, Cheo only managed to get 38.67% of the total votes.
With LKY's direct threats, a bias media, Chiam's attacks against SDP, HDB upgrading, gerrymandering etc all working against Ling and Cheo, both stood no chance of retaining their seats.
If you have more information, you should share it with us since you have been active in the political scene. But of course, you can continue to make baseless allegations without looking into the causes of their defeats and assert that their lost were due to them unable to sustain their initial political momentum. In a free speech environment here, you can say anything you like.