As the House prepares for a possible investigation of allegations concerning President Clinton, it’s worth taking a look back at how Congress has dealt with the frequent charges of misconduct by its own members. Here are 21 case studies. In most, Congress took little or no official action, leaving the fate of the accused to the voters. This history begins in 1974, but not because episodes of impropriety only go back a quarter-century. In the old days, they simply weren’t reported.