Every time Donald Trump celebrates curbing abortion rights, disdains compromising and advocates an “America First” foreign policy provides another window into the 21st-century transformation of the Republican Party.

It seems a lifetime since the GOP combined principled conservatives seeking to limit the federal government’s reach with moderates who joined with like-minded Democrats to advance civil rights, protect the environment and forge a bipartisan foreign policy.

An epitome of those moderates was Charles McC. (Mac) Mathias, a Frederick native who represented Maryland in the House and Senate from 1961-1987. He played a crucial role on national issues like the landmark civil rights laws of the 1960s and regional ones like the ecological restoration of Chesapeake Bay in the 1980s.

Besides being principled, he was a successful politician who comfortably won eight successive elections for state and national office and a skilled inside operator able to get results. His excellent staff members included Chris Van Hollen, who now holds his old Senate seat, and his 2010 eulogy was delivered by then Vice President Joe Biden.

Two former Mathias aides, Frederic Hill and Monica Healy, have produced a collection of essays entitled “Mathias of Maryland,” illustrating this self-styled Lincoln Republican’s role in the 20th Century GOP, before Newt Gingrich and Trump took it hard right and sharply confrontational. (I’ve known both for years and worked at The Sun with Hill.)

A life-long Republican, who supported his party’s presidential hopefuls from Barry Goldwater to Ronald Reagan, Mathias was, Hill notes, “one of the first and most outspoken Republican critics of Richard’s Nixon’s behavior and actions” in the Watergate scandal that led to Nixon’s 1974 resignation.

Before he died in 2010, Mathias recoiled at his party’s rightward lunge and, unable to accept John McCain’s choice of running mate Sarah Palin, voted for Democrat Barack Obama in 2008.

He reflected the more centrist politics that often prevailed in the years I covered Congress for Associated Press and The Baltimore Sun, along with respected Democrats like Montana’s Mike Mansfield and Minnesota’s Walter Mondale, and fellow Republicans like Pennsylvania’s Hugh Scott and New Jersey’s Clifford Case.

Here are the principal issues that reflect his career:

Civil rights. As a junior member of the House Judiciary Committee concerned about the Kennedy administration’s inaction, Mathias joined with future New York City Mayor John Lindsay and the panel’s ranking Republican, Rep. William McCulloch of Ohio, to introduce a comprehensive civil rights bill in early 1963. It “was the thing that stirred the Kennedy administration to finally get their bill drafted and introduced,” Mathias said, though highly publicized violence against rights demonstrations in Birmingham that Spring also spurred tits action.

Republicans like Mathias provided crucial support for passing the landmark 1964 Civil Rights Act, which desegregated public accommodations and barred employment discrimination, and the 1965 Voting Rights Act. As a senator, he played a major role in the 1982 action that strengthened the Voting Rights Act and extended key provisions for 25 years.

The environment. Mathias spent a decade generating support for federal action to protect the Chesapeake Bay, when he learned how pollution from industrial dumping was threatening the nation’s largest estuary’s ecological life, including its crabs and oysters. He succeeded in the 1980s when the government, led by a friendly Environmental Protection Agency administrator, William Ruckelshaus, set explicit goals for reducing pollution and Congress provided the necessary funds.

The Vietnam War. As a congressman, Mathias joined a dozen fellow GOP moderates in opposing President Lyndon Johnson’s escalation of the Vietnam War. His stance was a major factor in his 1968 upset victory over Democratic Sen. Daniel Brewster. Later, Mathias was active in bipartisan Senate efforts to force U.S. withdrawal from Vietnam.

He also played a leading role in establishing the Vietnam Veterans Memorial, working with Virginia’s Republican Sen. John Warner to overcome bureaucratic obstacles including Reagan Interior Secretary James Watt’s objections to aspects of the design.

Bipartisan foreign policy. Mathias was a strong supporter of arms control talks with the Soviet Union and maintaining close U.S. ties with its European allies. Casimir Yost, a Mathias’ foreign policy adviser, writes that the Maryland senator helped ease European concerns over President Jimmy Carter’s “mixed signals and homespun style’ and Reagan’s foreign policy intentions. He notes, as Senate bipartisanship eroded in the 1980s, Mathias correctly feared the Senate was becoming “dangerously fractured.”

Criminal Justice. Often part of bipartisan solutions, Mathias stood alone against a 1984 crime bill that adopted sentencing guidelines reducing the discretion of federal judges. He proved prescient in predicting it would lead to longer sentences and further overcrowding the “already bulging” federal prison system. According to Steven Metalitz, a Mathias staffer at the time, the prison population doubled in the next seven years. A key backer of the bill was Biden. “As it turned out, (Mathias) foresaw the future far better than Biden did,” Metalitz concludes.

South Africa sanctions. Mathias played a leading role in congressional approval of strengthened sanctions against South Africa’s apartheid regime, which passed over Reagan’s opposition. He also eased the tension when Biden clashed with Secretary of State George Shultz, sending a note to the future president that read, “Calm down, big fella, calm down.”

Biden cited the incident in his eulogy to Mathias, declaring, “He ended up leading the fight that succeeded in getting the very objective accomplished that I cared so deeply about.”

The bipartisanship strain that runs through the former Maryland senator’s work was a key to successful congressional action. Its virtual absence now explains much of today’s inaction.

Carl P. Leubsdorf (carl.p.leubsdorf@gmail.com) is a former Washington correspondent for The Associated Press and The Baltimore Sun and was Washington bureau chief of The Dallas Morning News.