Sen. John McCain, trying to solidify his support among conservatives amid resolute competition from former Arkansas Gov. Mike Huckabee, today won the endorsement of former President George Bush.

Welcoming "an old friend back to Texas," Bush called McCain -- who served as a Navy pilot during the Vietnam War and was captured and tortured by the Viet Cong -- "a remarkable patriot."

"Few men walking among us have sacrificed so much in the cause of human freedom," the former president said, adding that McCain has "the right values and experience to guide our nation forward at this historic moment."

Asked about conservative unease with McCain, the 41st president read from the diaries of former President Ronald Reagan, who was also assailed by the Right during his presidency for being "a turncoat." Bush dismissed conservative criticism of McCain as "an unfair attack," and said the Arizona senator has "a sound conservative record but not above reaching out to the other side,"

For his part, McCain, who has parted company from conservatives on immigration, taxes and campaign finance, said he welcomed the Bush endorsement and hoped it would help him rally the party behind him to begin waging a battle against Democrats.

"We as a party must unite and move forward and attract not only members of our own party but independents and so-called Reagan Democrats," McCain said, adding that Democrats had been wrong when they said the surge in Iraq would not work and should be held accountable for their position.

As McCain worked to tighten his hold on the Republican nomination, Democrats Hillary Rodham Clinton and Barack Obama were battling it out for votes ahead of Tuesday's Wisconsin and Hawaii primaries.