As reported by the Los Angeles Times, Jack Nicklaus has a motivation beyond pure politics for supporting Romney in this year's election: regret.
When Gerald Ford ran against Jimmy Carter in 1976, he asked for Nicklaus's support and involvement during the campaign. Nicklaus, in an effort to remain neutral, turned his friend and golf partner down.
“He asked me to get involved and I didn’t,” Nicklaus said. “I said, ‘Mr. President, I’ve always stayed away from politics. I deal with people on both sides.’ And he respected that and he never had an issue with that, and we played a lot of golf after that. But I didn’t help him and he lost Ohio by several thousand votes. Had he won Ohio, he would have won the election. I’ve always had big regrets about that."
“In spite of me not doing that, he paid me a great honor: I was a pallbearer at his funeral. He was such a good friend, such a nice man. That’s why I’ve gotten involved.”
UPDATE: Nicklaus didn't have all his facts correct. If Ford had won Ohio in '76, he still would have lost the election. Ohio's 25 Electoral College votes would have made Carter's margin of victory 272-265 instead of 297-240. Also, according to uselection.org, the difference was 11,000 votes.