"From 1789 through August 2010, Presidents submitted 160 nominations to Supreme Court positions. Of these, 36 were not confirmed by the Senate. The 36 nominations represent 31 individuals whose names were sent forward to the Senate by Presidents (some individuals were nominated more than once). Of the 31 individuals who were not confirmed the first time they were nominated, however, six were later nominated again and confirmed. The Supreme Court nominations discussed here were not confirmed for a variety of reasons, including Senate opposition to the nominating President, nominee's views, or incumbent Court; senatorial courtesy; perceived political unreliability of the nominee; perceived lack of ability; interest group opposition; and fear of altering the balance of the Court. The Senate Committee on the Judiciary has played an important role in the confirmation process, particularly since 1868."
CRS Report for Congress, RL31171