As the nation’s birthday nears, on Sunday the congregation at the Union Chapel in Oak Bluffs reflected on what it was like to live in America 50 years ago.

Lawrence O’Donnell, the MSNBC political late show host who was Sunday’s featured speaker, recalled the 1968 assassinations of Martin Luther King and Robert Kennedy, and said his cousin was among the thousands of Americans who died in Vietnam that year.

“Our family was one of the 16,899 families in 1968 who attended a military funeral. And it was just another day in America in 1968, a sickening day,” he said. “We had a feeling in 1968 that America had become a very different place.”

Union Chapel was filled nearly to capacity.

Jeanna Shepard

Union Chapel was filled nearly to capacity.

Jeanna Shepard

The former chief of staff of the Senate Finance Committee and former executive producer and writer for the NBC series The West Wing was the lay Sunday speaker in the chapel’s summer sermon series. His book, Playing with Fire: The 1968 Election and the Transformation of American Politics, came out last year.

Standing in the pulpit of the historic chapel where nearly every seat was filled, Mr. O’Donnell named each of the victims of the recent shooting at the Capital Gazette in Annapolis, Md.

“They cannot stand here today because they were murdered Thursday doing their jobs at their desks,” he said.

He described a certain “sickening feeling” pervasive in America on weeks like this, bemoaning the president’s rhetoric characterizing the press as the “enemy of the people.” But he also offered a wider view and said progress is everywhere, particularly in the election of President Obama, a feat many in 1968 would have called impossible.

“The truth of our history is that we have been in worse places than we are this week,” Mr. O’Donnell said.

He described the surviving journalists at the Capital Gazette, who in the midst of their shock and grief at the shooting, put out a paper the next day.

Trading in his television studio for a pulpit, Mr. O’Donnell struck a prayerful tone.

“That is the American spirit and that’s the spirit that’s going to prevail,” he said.

The president of the chapel’s board of trustees, Richard Taylor, also reflected on patriotism in the face of America’s flaws in his morning greetings.

He recognized Joann Kidd, who was present in 1965 at the civil rights march in Selma, Ala. He asked veterans in the congregation to stand, and the chapel filled with lengthy applause. Mr. Taylor later recognized Keisha Lance Bottoms, the recently elected mayor of Atlanta, who attended the service.

“While we acknowledge our perfect imperfections as a country, we still live in the greatest country on earth,” he said.

More information about the Union Chapel Sunday sermons can be found at unionchapelmv.org.