Park Chung Hee's government of South Korea (from his 1961 coup to his assassination in 1979) is usually thought of as extremely authoritarian, and this was certainly true after the 1971 declaration of the state of emergency and the 1972 adoption of the Yushin Constitution.
http://en.wikipedia.org/wiki/Fourth_Republic_of_South_Korea Even in the 1960's there was considerable repression. Nevertheless, the 1963 presidential election--which marked the transition from Park's holding power as head of a military junta to his doing so as elected president--was vigorously contested and very close:
Park Chung Hee Democratic Republican Party 4,702,640 46.6%
Yun Bo-seon Civil Rule Party 4,546,614 45.1%
Oh Jae-young Independent 408,664 4.1%
Byun Young-tae Righteous Citizens Party 224,442 2.2%
Jang I-seok New Development Party 198,837 2.0%
http://en.wikipedia.org/wiki/South_Korean_presidential_election,_1963
Who was this Yun Bo-seon who almost defeated Park? (To Google him, you should also look up "yun posun" and "yun po sun"...) He had been Mayor of Seoul and later Minister of Commerce and Industry under Syngman Rhee but became disillusioned with Rhee's authoritarian rule, and helped form the opposition Democratic Party to oppose Rhee's Liberal Party. BTW, in *both* 1956 and 1960, the Democratic Party presidential candidate (Shin Ik-hee in 1956, Cho Pyong-ok in 1960) died too close to the election to allow the party to name a replacement, so Rhee won easily. (And in both cases the death really does seem to have been of natural causes, with no evidence of foul play by Rhee. Think how implausible all this would seem if it were an alternate-history scenario! Incidentally, Shin Ik-hee's having been dead for ten days didn't prevent him from getting 1,800,000 votes in 1956, but all ballots cast for him were ruled invalid.)
The 1960 election was soon seen to be a fraud, not because of Rhee's (unopposed) victory but because of the official declaration that, contrary to all popular expectations, the Liberal Party's vice-presidential candidate, Lee Ki Poong, had defeated the Democratic Party's candidate (and incumbent) Chang Myon [1] by 79.2% to 17.5%. Protests against this obviously fabricated result led to the April Revolution that overthrew Rhee. The Democratic Party easily won the June 1960 parliamentary election (the Liberal Party disintegrated once Rhee was toppled). The new parliament in August elected Yun Bo-seon president. However, as South Korea had switched to a parliamentary system in response to Rhee's authoritarian excesses, the real power was in the hands of the Premier, Chang Myon. The Second Republic under Chang's leadership was short-lived: and was overthrown in the May 16, 1961 coup led by Park Chung Hee:
"The Second Republic was beset with problems from the start, with bitter factionalism in the ruling Democratic Party competing with implacable popular unrest for the government's attention. The South Korean economy deteriorated under heavy inflation and high rates of unemployment, while recorded crime rates more than doubled; from December 1960 to April 1961, for example, the price of rice increased by 60 percent, while unemployment remained above 23%. Widespread food shortages resulted. Chang Myon, meanwhile, representing the Democratic Party's 'New Faction', had been elected Prime Minister by the thin margin of three votes. Purges of Rhee's appointees were rendered ineffective in the public eye by Chang's manipulation of the suspect list to favour wealthy businessmen and powerful generals. Although Rhee had been removed and a democratic constitution instituted, the 'liberation aristocrats' remained in power, and the worsening problems facing South Korea were proving insurmountable for the new government."
http://en.wikipedia.org/wiki/May_16_coup
Park Chung Hee did allow Yun to stay on as figurehead president for a while, but Yun resigned on March 22, 1962. Later that year, Park had a new constitution adopted which provided for a return to presidential government. (Park at first promised not to run in the forthcoming presidential election, but went back on this.) The election was held in October 1963, and as noted, Park won only very narrowly, and with less than a majority. He carried the rural areas by just enough votes to offset Yun's advantage in Seoul and other cities.
Why did Park win at all? Part of the reason was that the election, though certainly free compared to Rhee's rigged elections of 1960 or to any subsequent South Korean presidential election for decades to come, was not entirely fair:
"Park enjoyed a clear advantage over the opposition in terms of organization and campaign funds. He used the state bureaucracy, including the police, extensively to mobilize votes. The myriad parastatal organizations like the NACF [National Agricultural Cooperatives Federation--DT] and the PMNR [People's Movement for National Reconstruction--DT] also actively joined his election campaign, enabling the DRP [the Democratic Republican Party, Park's party--DT] to reach deep down into the villages for support. Although it was caled 'the freest and fairest election in [South] Korean history', the 1963 presidential election was marred by irregularities. By ruling that the MHA [Ministry of Home Affairs]-appointed head of a rural village was not a civil servant, and thus was free to join political parties and conduct campaign activities. The heads of rural villages and urban blocs were on the public payroll, but freely canvassed households to solicit support for Park...
"The September and October issues of *Chosun Ilbo* carried reports of irregularities every day. Some village heads forced farmers to apply for DRP membership under the threat of abruptly ending their grain rations. County officials and policemen were transferred to their hometowns before the election to persuade families and friends, apparently in accordance with an MHA directive. The Seoul City police department was found to be asking its officers to submit a list of relatives and local notables with the power to influence the vote in their hometowns...
"In the end it was the countryside that came to Park's rescue. The DRP candidate carried 50.8 percent of the rural vote, whereas Yun Po-son garnered 57.1 percent of the urban vote..."
https://books.google.com/books?id=DTW1UdHLWUYC&pg=PA354
Park's victory in the rural areas was no doubt in part due to the bureaucratic advantages mentioned above, but it also had to do with the fact that the farmers had been treated badly under prior governments (including the Chang Myon government Park had overthrown), whereas Park projected an image of caring about the farmers, with a program of rural debt relief and a temporary boost in 1962 in the price the state paid for rice. After the election, Park was to give agriculture a low priority (and even in 1963 he partially reversed his 1962 price support policy due to fear of inflation) but as of 1963 farmers still thought he was basically friendly to agriculture.
And yet, with all these things going against him, Yun almost won. Suppose he had won? (POD? Maybe if one of the minor candidates had endorsed him--after all, Park got substantially less than 50 percent of the vote.) Would this have saved South Korea from Park's increasingly authoritarian rule, and if so, would it have been at the expense of the economic development Park brought? The problem is that Yun was only a figurehead in 1960-62, so we don't really know how he would govern under a presidential constitution. (Although the very fact that he acquiesced so readily in Park's coup and stayed on as figurehead president for a while does not give the impression of an especially strong personality...) My suspicion, however, is that his newly cobbled together Civil Rule Party, even if it won a majority of seats in parliament, would no more stay united than the Democratic Party had been during its brief taste of power in 1960-61, and that intra-party squabbles and government inefficiency would provide the excuse for another military coup. (Would such a coup be led by Park, though? I doubt it. Park formally resigned from the army in 1963. My feeling is that his losing the election--with all the advantages he had--would have so discredited him that if there were to be a coup against Yun Bo some other military man would lead it. But I really don't know much about South Korean military politics of this era--though I do remember reading that in the early 1960's the army was still very factionalized).
Incidentally, 1963 was probably Yun's last real chance; he ran again in 1967, but lost to Park more decisively (51.4-40.9).
http://en.wikipedia.org/wiki/South_Korean_presidential_election,_1967
Thoughts?
[1] He had been elected vice-president in 1956, defeating Rhee's candidate, Lee Ki Poong (Yi Ki-bung). Remember that Rhee himself had only gotten 55% of the vote in that election if you count the ballots cast for the deceased Shin Ik-hee. (The official result in the 1956 presidential election, with the votes for Shin not included, was 70% for Rhee, 30% for the independent Cho Bong-am, who opposed Rhee's "March North" slogan and advocated peaceful reunification. Opposition from Cho Bong-am was not a problem for Rhee in 1960 because he had him executed in 1959 for alleged contacts with North Korean agents. Cho's name was finally posthumously cleared by the South Korean Supreme Court in 2011.
http://english.khan.co.kr/khan_art_view.html?code=790101&artid=201101211819057 )
Anyway, Rhee was getting on in years--he was 85 in 1960. It seemed likely that whoever was elected vice-president would succeed him in office. (Though in fact Rhee didn't die until 1965, so maybe he would have served out his term after all--though perhaps not, if only because continuing in the presidency might be harder on his health than OTL's enforced exile in Hawaii.) For this reason, he was absolutely determined that Lee would defeat Chang this time (though even some Liberals after 1956 had wanted to dump Lee because of his unpopularity and his association in the public mind with police repression) and obviously he engaged in some overkill:
"Once more Rhee's reelection was assured in the absence of a serious opponent. With Rhee's age as a factor, the vice-presidential race was more important...In the election, opposition campaign workers were repeatedly arrested and beaten. Hoodlum members of the Anti-Communist Youth Corps were present in alternate voting booths to see how the citizen cast his ballot. In many rural areas, three-man and nine-man 'teams' were formed, with the 'head' of each team, whose loyalty to the Liberal Party was unquestioned, ensuring that the other 'team members' voted for the Liberal candidates. The police were openly in support of the Liberal candidates.
"As it turns out, such efforts were not necessary, because the election results were completely fabricated by police headquarters and the ministry of internal affairs..."
Sung-ju Han, *The Failure of Democracy in South Korea* (Berkeley: University of California Press, 1974), p. 28.
https://books.google.com/books?id=UsVWcfLo1t4C&pg=PA28