I’m surprised you don’t remember the John Tower situation under the first President Bush. It’s included in the list provided by Ravenman.
It was a big deal – apparently it had been discovered that Tower had a drinking problem – and it wasn’t that long ago.
Ed
Well, with all due respect, that was 12-16 years ago, when I was a young ivysprig and not at all interested in politics. 
Sorry about that. To me, the first Bush administration feels like it was just yesterday, and the Reagan administration was last week. I turned 18 in 1980.
And yet I still consider myself a child prodigy!
Ed
This is what opponents of Lani Guinier claimed her articles said. Guinier’s opponents wanted the public to believe she was in favor of a racial quota system in congress and labeled her with the epithet “quota queen.” In fact, all Guinier did was write papers on proportional representation, a system that has nothing to do with quotas, congressional districts for minorities or veto power by minorities. She later published the papers in a book titled Tyranny of the Majority: Fundamental Fairness in Representative Democracy .
Proportional representation is a system in which legislative seats are won by political parties in proportion to the vote the parties receive. For example, if the Libertarian Party got five percent of the vote, it would get five percent of the representation in the legislature. While such a system would allow for greater representation of small parties, it is in no way a quota system, nor does it have anything to do with race.
Clinton withdrew Guinier’s appointment when the controversy around her got too hot. He said he did it based on a reading of her papers, but I’ve always suspected his main motivation was political expediency.