Souter was a Republican appointed by President George H.W. Bush in 1990, largely on the recommendation of New Hampshire's former Gov. John Sununu, who had become the first President Bush's chief of staff.
But Souter surprised Bush and other Republicans by joining the court's more liberal wing.
He generally votes with Stevens and the two justices who were appointed by President Bill Clinton — making up the bloc of four more liberal members of the court, a group that has usually been in the minority throughout Souter's tenure.
It is also believed that Souter waited to make sure no one else was planning to retire imminently before making this announcement, which means that no matter who Obama chooses, it should not affect the tone of the decisions made by the Supreme Court, at least not during the next court term, unless one of the more conservative Justices decides to retire or falls ill.
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