Two months ago, Modi and his Bharatiya Janata Party (BJP) celebrated their first year in office, trumpeting initiatives introduced to reform Asia's third largest economy and proclaiming the government scam free.
But just weeks later, embarrassing allegations ensnared Foreign Minister Sushma Swaraj along with the chief ministers of Rajasthan and Madhya Pradesh where the right-wing BJP rules at the state level.
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Analysts say the government's credibility risks damage after it pledged an honest and efficient administration, to attract much-needed foreign investment and win over voters enraged about endemic corruption.
Graft scandals plagued the previous Congress-led government, resulting in policy paralysis and the worst economic slowdown since the 1980s.
The latest allegations also threaten Modi's critical land, taxation and other legislative reforms, with this week's new session of parliament erupting in chaos over opposition demands for Swaraj and the chief ministers to resign.
"These scams that have broken out have really lowered the image of the BJP-led government," said Satish Misra, a senior fellow with the Delhi-based Observer Research Foundation think tank.
"BJP leaders celebrated their first year with a lot of pomp and show, saying 'we have no scams, we are incorruptible'. But in the 13th month, there were scams breaking out everywhere," Misra told AFP.
The government has staunchly resisted calls to sack Swaraj over her role in helping corruption-hit former cricket boss Lalit Modi obtain a passport in the UK.
The BJP has stood behind Rajasthan chief minister Vasundhara Raje, under fire for allegedly supporting Lalit Modi's UK immigration application while he was under investigation back in India for graft.
But it is also under pressure over Shivraj Singh Chouhan, chief minister of Madhya Pradesh state, where thousands of people are alleged to have bribed officials and politicians in return for jobs or places in training institutes.
India's top court has ordered a federal investigation into the so-called Vyapam scam after a spate of recent deaths fuelled claims of a mass cover-up by the Chouhan government.
The opposition says dozens of people associated with the scam, including witnesses, have died but state authorities say there is little evidence to connect any of the deaths or to suggest foul play.
Separately, a court has agreed to look into an allegation that national education minister Smriti Irani lied about her education degree.
As parliament began on Tuesday, the prime minister appealed for opposition unity to push through his long-awaited new national sales tax and other reforms.
"We all have to work together to take important decisions for the development of the nation," Modi told reporters.
But a veteran BJP leader, lawmaker Shanta Kumar, broke ranks, calling for an ethics committee to be set up to investigate some of the scandals embroiling the BJP leaders.
"News about the Vyapam scam in Madhya Pradesh has made us hang our heads in shame," Kumar, a former chief minister of Himachal Pradesh state, wrote in a letter to BJP president Amit Shah.
"It's natural for any Indian to feel disappointed and disheartened with the kind of news on the front pages of newspapers and TV channels," he said in the letter, released this week on his Facebook page.
Parliament descended Thursday into turmoil for a third straight day, with the government branding opposition demands for resignations irresponsible, saying none of the BJP leaders had broken any laws.
Lacking a majority in the upper house, the BJP needs opposition support to pass its bills including the goods and services tax (GST), which harmonises a myriad of state and central levies.
Modi, who has a reputation as a strong leader and an efficient administrator, has pledged a plethora of such reforms to erase India's reputation as an unpredictable and corrupt place to do business.
During the one-year celebrations in May, BJP chief Shah told the Times of India newspaper that under Modi "not a single scam has happened. That shows there's no corruption."
But analysts say foreign investors will be monitoring the new turmoil with concern, despite the fact no BJP leader has been charged with any wrongdoing.
"I would not say they (investors) are deserting India but they would be keenly watching this," the Observer Research Foundation's Satish Misra said.
However, analyst Sanjay Kumar said the scandals were not severe enough to sway public opinion.
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"The previous government set the benchmark for scandals and the BJP ones don't come close," said Kumar, director of the Centre for the Study of Developing Societies in Delhi.
"The BJP's image has been dented and they are finding it difficult, but they can bounce back."
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