Former New York Sen. Al D'Amato abandoned his summer endorsement of Fred Thompson and publicly backed John McCain Tuesday for the GOP presidential nomination, after Thompson dropped his presidential bid following a third place showing in the South Carolina primary.

D'Amato endorsed Thompson in June, as the hype surrounding the former Tennessee senator's presidential bid was reaching a fever pitch. But Thompson's popularity in the polls steadily declined after he announced his run in September.

D'Amato's latest endorsement also draws to the surface a past feud between the former senator and his fellow New Yorker, former New York City Mayor Rudy Giuliani.

D'Amato and Giuliani have had friction dating back to 1994, when Giuliani crossed party lines to endorse Democrat Mario Cuomo for governor over then state Sen. George Pataki, who D'Amato was supporting.

D'Amato and McCain, however, have been close since their Senate days together.

"If you want to win in November, John McCain is the man," D'Amato said, calling the senator a national treasure and a true hero. "This is a man whose time is here, who can restore confidence and people can have confidence in what he says."

McCain, who won the South Carolina primary and has been campaigning in Florida ahead of its Jan. 29 primary, flew to New York Tuesday to pick up the endorsement and raise money on Giuliani's turf.

A D'Amato endorsement could be a nudge for McCain in a delegate-rich state where he and Giuliani are tensely competitive.

A Quinnipiac University poll from Jan. 14-21 showed McCain and Giuliani tied in New York at 30 percent each. The state holds its primary Feb. 5. The poll interviewed 331 likely primary voters, and had a margin of error of 5.4 percent.

FOX News' Carl Cameron and Malini Bawa and The Associated Press contributed to this report.