Nehru was a leader recognized in world politics which made him a choice for being PM. I have read about his affairs but that doesn’t challenge his leadership capabilities. The only thing he did wrong was underestimating China and playing fool there but he was confident of US and USSR backing him there so he played that strategically but it backfired.
Now coming to the PM who did most damage to the country, Indira Gandhi stands out as an obvious answer. She was an example of anarchist to the core.
A recap of all the wrong she did back then:-
1) Winning election by fraud and when found guilty she declared emergency and put everyone in jail who spoke against her.
2) Bluestar operation, first creating a terrorist and then doing something so reckless which alienated a community.
3) Indira closed the economy of India, had she made the right choice then this country would have been a different place altogether.
4) She pushed country back to where Nehru Ji left and Shashtri Ji picked it by a closed economic approach, Favoritism and her best punch Emergency.
Relationship with Pak were already bitter and she did not do any good
by fighting 1971 war though I am not totally against her helping create Bangladesh but that was done in not the best strategic fashion. In fact she did it successfully but at the cost of a lifetime of animosity from a neighboring country. Also now Bangladeshi terrorism is catching up at a good speed.
No doubt she was ballsy but she was a bad leader because she had no convictions, she could not handle a crisis and she could not deal with critics. More importantly, she lacked the ability to build a team of talented people in the party and in the government. She wanted trusted lieutenants and she had plenty of them around.
Manmohan Singh can be called another obvious choice for a bad PM because he did nothing except all the effort he put in saving one of the most corrupt family of India.
1) He was Prime Minister and there was corruption going on in ministry directly under him and he kept his eyes closed.
2) He took no action except speaking occasionally agaisnst Pak’s ceasefire, murder of soldiers, terrorist attacks.
3) He was(and is) a sharp and shrewd economist and his best answer to rising inflation, rate of fuels and commdoities was “Coalition government has its own challenges”.
He never even tried to motivate people like a leader. He was merely put there as an honest face to win election for his clean image which worked well in 2009. He was a terrible and a spineless leader.