Former New York Mayor Rudy Giuliani has pulled out of the Republican race for the White House after disappointing primary results in Florida, BBC reported.
Giuliani announced he was giving his support to Arizona Senator John McCain, describing him as "an American hero".
Governor Arnold Schwarzenegger of California will also endorse Mr McCain.
Earlier on Wednesday, Democrat John Edwards left the race, without backing any of his rivals, after failing to win a single party nomination contest.
Edwards contested Iowa, New Hampshire, Nevada and his native South Carolina, but only in Iowa did he get higher than third place, and that only by the narrowest of margins.
He told supporters in New Orleans, where he launched his latest White House bid in 2006: "It's time for me to step aside so that history can blaze its path."