Here’s a good read. ForeignPolicy.com: “Will India’s Next Leader Be Banned From America?”
My Summary: In 2005, the US State Department banned a state-level Indian politician, Narendra Modi, Chief Minister of Gujarat, from coming to the United States due to his alleged role in genocidal activities against Muslims (though investigations in India have never officially tied him to them) during the February 2002 riots in Gujarat. State figured it would be a symbolic denunciation with few likely consequences down the road.
Fast forward to present and now he is a national leader of the main opposition party (the Hindu nationalist BJP) and is widely anticipated to cruise into the office of prime minister next year. Now, the State Department is on the fence about what to do, particularly since he hasn’t been elected yet. Lifting the ban now would be seen as an endorsement or interference. Lifting it after he wins (if indeed he does) would be embarrassing and make the State Department look like it was bending the rules.