Pete McCloskey — a pro-environment, anti-war California Republican who co-wrote the Endangered Species Act and co-founded Earth Day — has died. He was 96.

A fourth-generation Republican “in the mold of Teddy Roosevelt,” he often said, McCloskey represented the 12th Congressional District for 15 years, running for president against the incumbent Richard Nixon in 1972. He battled party leaders while serving seven terms in Congress and went on to publicly disavow the GOP in his later years.

ON THIS DAY IN HISTORY, AUGUST 8, 1974, PRESIDENT NIXON ANNOUNCES HIS RESIGNATION

He died at home Wednesday, according to Lee Houskeeper, a family friend.

Years after leaving Washington, McCloskey made one last bid for elective office in 2006 when he challenged Richard Pombo of Northern California’s 11th District in a primary race that McCloskey described as “a battle for the soul of the Republican Party.” After losing to Pombo, who had spent most of his tenure in Washington attempting to undo the Endangered Species Act, he threw his support behind Democrat Jerry McNerney, the eventual winner.

“It was foolish to run against him (Pombo), but we didn’t have anybody else to do it, and I could not stand what a—— they’d become,” the frank-talking former Marine colonel said of the modern GOP in a 2008 interview with The Associated Press.

McCloskey cited disillusionment from influence peddling and ethics scandals under the George W. Bush administration as reasons why he switched parties in 2007 at the age of 79. “A pox on them and their values,” he wrote in an open letter explaining the switch to his supporters.

“McCloskey was a rarity in American politics — his actions were guided by his sense of justice, not by political ideology,” Joe Cotchett, his law partner since 2004, said in a statement. “He hated inequity and did not hesitate to take on members of his own political party.”

Born in Loma Linda, California, on Sept. 29, 1927, as Paul Norton McCloskey Jr., he graduated from South Pasadena High School, where the second baseman made the school’s baseball hall of fame, although he self-deprecatingly called himself “perhaps the worst player on the baseball team.”

McCloskey joined the Marine Corps as an officer and led a rifle platoon during some of the most intense fighting of the Korean War. He was awarded the Navy Cross for extraordinary heroism, the nation’s second-highest honor, a Silver Star for bravery in combat and two Purple Hearts.

He earned a law degree from Stanford University and founded an environmental law firm in Palo Alto before making the move to public office. In 1967, he defeated fellow Republican Shirley Temple Black and Democrat Roy Archibald in a special election for the San Mateo County congressional seat.

The left-leaning McCloskey had a thundering presence in Washington, attempting to get onto the floor of the 1972 Republican National Convention during his bid to unseat then-President Nixon on an anti-Vietnam War platform. He ultimately was blocked by a rule written by his friend and law school debate partner, John Ehrlichman, that said a candidate could not get to the floor with fewer than 25 delegates. McCloskey had one.

Still, McCloskey loved to say he finished second.

He would later visit Ehrlichman in prison, where Nixon’s former counsel served 1.5 years for conspiracy, perjury and obstruction of justice in the Watergate break-in that led to the president’s resignation.

While in office, McCloskey also was known for befriending Palestinian leader Yasser Arafat and criticized Israeli influence on American politics. The congressman was the first to demand Nixon’s impeachment, and the first to demand a repeal of the Gulf of Tonkin resolution that allowed the Vietnam War.

But his enduring legacy is the Endangered Species Act, which protects species designated as endangered or threatened and conserves the ecosystems on which they depend. McCloskey co-wrote the legislation in 1973, after a campaign by young people empowered by Earth Day activities successfully unseated seven of 12 Congress members known as “The Dirty Dozen” for their anti-environment votes.

“On that day, the world changed,” McCloskey recalled in 2008. “Suddenly, everybody was an environmentalist. My Republican colleagues started asking me for copies of old speeches I had given on water and air quality.”

“A powerful champion of endangered species, Pete, ironically, became one,” said Denis Hayes, co-organizer of the Earth Day, about the rarity of a “green, anti-war Republican.”

After 15 years in the House, he lost his run for a Senate seat to Republican Pete Wilson, who went on to be California’s governor. He moved back to rural Yolo County, relishing the life of a farmer and part-time attorney.

“You know, if people call you ‘congressman’ all the time, you’ll end up thinking you’re smarter than you are,” he said.

McCloskey, however, couldn’t stay quiet forever.

In 2006, after his unsuccessful race against Pombo, he helped form the Revolt of the Elders Coalition, a group of retired Republican congressmen who pushed to get soldiers more money for college, undo measures that made it tougher to investigate ethics violations and rallied against those who had received funding from disgraced lobbyist Jack Abramoff, including Pombo.

“If you can do something at age 80 that positively affects our country, you should be proud of it. Otherwise there’s no redeeming value in getting older,” he said.

McCloskey is survived by his wife, Helen — his longtime press secretary whom he married in 1978 — and four children by his first wife: Nancy, Peter, John and Kathleen.