Singapore Democratic Party (SDP) chief Chee Soon Juan, 53, has made four unsuccessful bids to enter Parliament since going into politics in 1992.
Eight months ago in GE2015, his four-man team in Holland-Bukit Timah GRC polled 33.4 per cent, a result he described as "dismal".
It was slightly higher than the 30.1 per cent of eligible Singaporeans who voted against the ruling People's Action Party (PAP) nationwide.
Come May 7, Dr Chee will be making another attempt at getting elected.
His stump speeches at last year's general election drew crowds. Also notable at the hustings was his shift away from his adversarial style of politics of the past, which included a hunger strike in 1993 and heckling former prime minister Goh Chok Tong at a hawker centre before GE2001.
Last year, Dr Chee pledged instead to find common ground and work with the PAP. And so, this by-election becomes the latest test - after GE2015 - of how accepting voters are of his makeover and chequered political past, observers say.
If he does not succeed in his bid, political watchers suggest that anything less than a 40 per cent vote share will constitute a poor result, especially with the "by-election effect" in play to some extent.
Former Nominated MP Eugene Tan says: "The interesting thing is to see how voters will respond to his outreach and his new image.
"If Dr Chee is unable to secure a good score, it shows he still has quite some way to go. The question, then, is whether he will ever shake off his previous image."
UniSIM College senior lecturer Walter Theseira says Dr Chee has stronger name recognition compared with his opponent, lawyer Murali Pillai, 48 - a "relatively new PAP face" who entered the public limelight on account of his first electoral contest in Aljunied GRC last year. So it is a golden opportunity for Dr Chee to show he can "translate his name recognition and personality into votes".
"If Dr Chee polls in the low 30 per cent range, it will not be a good performance for an opposition party leader in such a one-on-one fight."
National University of Singapore (NUS) political scientist Bilveer Singh's assessment is harsher. He thinks a loss could "tarnish Dr Chee's political image and may even open up doors for a potential power struggle within the SDP".
The impact of Dr Chee's past could cut both ways.
While there might still be some distrust, Dr Singh's NUS colleague Hussin Mutalib says there may also be "voter sympathy for his long and arduous struggle - they may wish to give him a chance".
Dr Chee had to sit out two general elections when he was made a bankrupt after a defamation suit brought by Mr Goh and the late founding prime minister Lee Kuan Yew over remarks he made during GE2001. He was discharged in 2012 after both men accepted his offer of settlement.
Still, Institute of Policy Studies deputy director for research Gillian Koh says the nine days of hustings "can throw up different things, which means the SDP camp has to be careful to remain electable in the eyes of the residents".
Some Bukit Batok residents, like polytechnic student Toby Chua, 24, said they found Dr Chee's campaign slogan "Now Is The Time" and online presence appealing.
The SDP has outlined a series of alternative policies. Some, like freedom of speech, struck a chord with lecturer Judy Tham, who is in her 40s. She says: "Dr Chee has proven himself to be someone with a level of intellect who can speak for us, and he is someone who means what he says."
Given the high-profile lapses in governance and accounting practices that dogged the Workers' Party-run town council, it is telling that the SDP has moved to assuage residents' concerns about its abilities by forming a panel to help oversee handover matters in the first 100 days, should Dr Chee win.
Says Dr Norshahril Saat of the Iseas-Yusof Ishak Institute: "They (SDP) understand the need to ensure they do not repeat the mistakes of the opposition party in Parliament, and want to convince voters they can run the town council."
Still, Dr Singh says Dr Chee's message in the by-election continues a familiar narrative: that he will be a more effective voice than his PAP rival - who Dr Chee says will echo the party line.
It is not a line that will sway Bukit Batok residents, adds Dr Singh, because if Dr Chee is elected, he will be one man up against the ruling party machinery.
Dr Koh and Dr Theseira argue that last year's weaker performance by the opposition does not signify a waning in the voters' desire for more political plurality in Parliament.
Says Dr Theseira: "The question is whether they want those voices to come from the SDP and Dr Chee in particular. This by-election is a test of that proposition."
- Additional reporting by Ng Keng Gene and Samuel Mak