1952 Lok Sabha Election - Indian National Congress won 364 seats out of the total 498. Reason - Weak opposition, powerful image of Jawaharlal Nehru, Congress party got strong support from almost every class specially from upper castes, dalits and muslims.
1957 Lok Sabha Election - Indian National Congress won 371 seats out of the total 494. Reason - Weak opposition, popular image of Jawaharlal Nehru, Congress party was favoured among upper castes, dalits and muslims.
1962 Lok Sabha Election - Indian National Congress won 361 seats out of the total 494. Reason - Weak opposition, powerful image of Jawaharlal Nehru, Congress party received support from upper castes, dalits and muslims.
1967 Lok Sabha Election - Indian National Congress won 283 seats out of the total 520. Congress Party lost 67 seats and about 4% votes as compared to the last general election due to some internal conflicts and low growth rate (mainly due to the 1962 war with China and 1965 war with Pakistan), Lal Bahadur Shastri in his very small tenure made some great efforts, he delivered good governance but Congress suffered and lost some seats, still Congress won the election with healthy majority. Congress party was still receiving good support from the upper castes, dalits and muslims, and opposition was also struggling. Indira Gandhi daughter of popular Jawaharlal Nehru was leading the Indian National Congress which helped Congress and her to become Prime Minister.
1971 Lok Sabha Election - Indian National Congress won 352 seats out of the total 518. This time they improved by winning large number of seats, but Congress got divided and Indira faced tough challenges from her opponent party called Indian National Congress(Organisation) which was formed after the split of Congress Party, INC(O) received fine support by winning 51 seats and by earning 24.34 % votes, Indira Gandhi campaigned very hard for this election, she was still very popular and she once again proved her power by winning the election with clear majority.
1977 Lok Sabha Election - Indian National Congress won 189 seats out of the total 542. Congress led by Indira Gandhi got defeated badly this time, Janta Party won the election Morarji Desai was chosen as the Prime Minister and thus he became India's first non-congrees Prime Minister. Main reason for her defeat was The Emergency. She lost her popularity in states like Bihar, Uttar Pradesh, Delhi, Gujarat, Madhya Pradesh, West Bengal, Rajasthan, Odisha, though she recieved good support from south Indian states. Jayaprakash Narayan's Total Revolution became successful and JP united all opponent parties and build strong Janta Party to defeat Indira Gandhi. At that time people were suffering from issues like misrule, unemployment, and corruption.
1980 Lok Sabha Election - Indian National Congress won 374 seats out of the total 542. Indira Gandhi again came to the power by winning handsome number of seats. Janta Party got divided into pieces due to the internal conflicts and greed. Janta Party became weak, opposition of Congress got fractured, this boosted Congress Party, people again started voting for the Congress and Congress again became strong.
1984 Lok Sabha Election - Indian National Congress won 404 seats out of the total 533. This election happened soon after the assassination of powerful Prime Minister Indira Gandhi. Congress won huge seats, Rajeev Gandhi who was the son of Indira Gandhi received massive support from the voters. Upper castes, Dalits, Muslims, supported him and his party.
1989 Lok Sabha Election - Indian National Congress won 197 seats out of the total 545. Congress Party lost 207 seats and about 9% votes as compared to the last general election. This time V.P Singh's party Janta Dal got allied with many strong regional political parties like TDP, DMK, AGP, and formed the National Front to challenge the Congress Party of Rajiv Gandhi. Janta Dal won total 143 seats and BJP for the first time was successful in winning 83 seats in that election, BJP supported VP Singh's government from outside, Communist Party of India also supported the VP Singh and thus V.P. Singh became the Prime Minister. Congress lost this election because Rajiv Gandhi did not performed anything special, his governance was not impressive, people were suffering from the issue of corruption, his government from (1984–89) did not created any big change. Stand on Ayodhya helped BJP, BJP received support from Upper caste Hindus and other Hindu nationalist in Indian states like Bihar, UP, Gujarat, Himachal, MP.
1991 Lok Sabha Election - Indian National Congress won 244 seats out of the total 545. After first round of the polling the assassination of Rajiv Gandhi happened. The congress party did bad in the pre-assassination constituencies and swept the post-assassination constituencies. A minority Congress-led government (with the help of left parties) led by P.V. Narasimha Rao was formed.
1996 Lok Sabha Election - Indian National Congress won 140 seats out of the total 545. P.V Narasimsha Rao helped to fix the Indian Economy but his government faced many charges of corruption and misrule. BJP joined hands with strong regional parties like Shiv Shena, HVP, Samta Party. BJP campaigned about the role of Hindutva in its vision for India, advocated self reliance in economy and security. BJP led by Atal jee got 161 seats but result of the election was hung parliament. BJP formed a short lived government. H.D. Deve Gowda became the PM from the Janta Dal with the support of left parties and Congress. Large section of Hindu voters who once used to vote for Congress in past elections started shifting towards the BJP.
1998 Lok Sabha Election - Indian National Congress won 141 seats out of the total 545. Congress left the United Front and new election happened. After the result of that election no political parties able to form strong alliance. BJP was growing fastly and they got 182 seats, at last BJP formed the government with 286 members but Vajpayee's government got collapsed once again in late 1998 when the AIADMK withdrew their support.
1999 Lok Sabha Election - Indian National Congress won 114 seats out of the total 545. NDA led by Atal Bihari Vajpayee formed the government, BJP won 182 seats once again. Congress failed again and BJP was improving.
2004 Lok Sabha Election - Indian National Congress won 145 seats out of the total 543. Congress returned to the power with the help of its allies. BJP won 138 seats in this election but support from strong regional parties like BSP, SP, and the left front helped Congress to gain the power, Dr. Manmohan Singh became the Prime Minister. Left front and strong regional allies saved the Congress. But BJP was still there in the picture.
2009 Lok Sabha Election - Indian National Congress won 206 seats out of the total 543. United Progressive Alliance helped Congress. Manmohan Singh again became the PM of India with the support of regional parties like RJD, BSP, SP.
2014 Lok Sabha Election - Indian National Congress won 44 seats out of the total 543. NDA led by Narendra Modi won sweeping victory. BJP won 282 seats 31% votes and Congress won only 19.52% votes. I don't need to mention about the Corruption scandals made by UPA-2 and about the wave of Modi.
According to my observations Indian National Congress failed because of -