Supporters of a bipartisan overhaul of the country’s immigration laws lost a standard-bearer in Sen. John McCain, who died at 81 on Saturday following a battle with brain cancer.

Still, the Arizona Republican left an indelible mark on the hyperpartisan debate that could offer current and future lawmakers an eventual blueprint for passing a sweeping immigration law.

“Whatever else historians will say about comprehensive immigration reform … McCain-Kennedy will remain central,” said Muzaffar Chishti of the nonpartisan Migration Policy Institute, referring to a 2005 bill authored with the late Massachusetts Democratic Sen. Edward M. Kennedy. “It became the symbol of what a good bipartisan approach to immigration should be.”

The bill was the first major proposal to combine a path to citizenship for undocumented immigrants living in the United States with increased border security, the formula that has since been the foundation of most bipartisan overhaul efforts. Kennedy, a close friend of McCain’s, died in 2009 of the same type of brain cancer that the Arizonan battled.

Mark Delich, who worked for McCain before joining FWD.us, the immigration advocacy group co-founded by Facebook executive Mark Zuckerberg, said in a statement that McCain’s “desire to solve this issue was one of practicality: to uphold the integrity of our immigration system, fill unmet labor demands, but also recognize the reality that 11 million people are living in this country and contributing to their communities, the majority [of them] for decades, without full protection of the law or an ability to become legal residents.”

In 2013, McCain was part of the so-called gang of eight senators whose immigration overhaul bill passed the chamber with 68 votes. The bill was never called up for a vote in the House, partially because of pressure from GOP hard-liners who opposed granting legal status to undocumented immigrants.

Following the 2016 election of President Donald Trump on a nationalist, anti-immigrant platform, McCain remained one of a shrinking number of pro-immigration voices among Republicans. He opposed Trump’s plan to end the Deferred Action for Childhood Arrivals program, which protects from deportation nearly 700,000 “Dreamers” who were brought to the United States as children, and called Trump’s family separation policy “an affront to the decency of the American people, and contrary to principles and values upon which our nation was founded.”

Still, McCain was not always impervious to the realities of politics and was sometimes forced to tack right on immigration, including as the Republican nominee for president in 2008. He was criticized by the campaign of former President Barack Obama, the Democratic nominee, for flip-flopping on the issue between the GOP primaries and the general election.

“Like with all politicians, it’s a complicated legacy,” Chishti said. “He had already sensed that immigration does not sell well in Republican primary politics and he caved to that.”

McCain also shifted right on immigration during his 2010 Senate re-election campaign, backing Arizona’s strict immigrant enforcement law known as SB 1070, which allowed police there to ask for immigration papers of anyone they arrested. McCain also ran a TV commercial calling for the completion of the “danged fence” on the U.S.-Mexico border.

But immigration hard-liners weren’t convinced. “McCain was hawkish at election time and dovish on immigration the rest of the time,” said Mark Krikorian, executive director of the right-leaning Center for Immigration Studies. “It was remarkably transparent.”

In “The Restless Wave,” his final memoir published earlier this year, McCain offered a blueprint for circumventing the hard-liners in his own party, including the conservative House Freedom Caucus.

“I’ve come to the conclusion that to get an immigration bill through Congress and to the president’s desk will require one of three things to happen. Either Democrats retake the House, or enough practical, problem-solving House Republicans vote for a discharge petition [to force a compromise immigration bill to the floor], or Republican leaders break with recent precedent and bring a bill to the House floor for a vote that offends the Freedom Caucus,” McCain wrote. “I’d vote for the latter, but it’s not in my power to arrange; more’s the pity.”

Niels Lesniewski contributed to this report.Watch: A Life in the Public Eye: A Look Back at McCain’s Congressional Career