Among the uninvited: members of the Westboro Baptist Church, who gathered a few blocks away from the cathedral. “MOST PEOPLE GO TO HELL” was among the few printable signs.

Gathering outside the Vietnam Veterans Memorial.

Dozens of people gathered around the Vietnam Veterans Memorial, forming a quiet ring on the outskirts of the wall before Ms. McCain arrived to honor her husband and other veterans of the Vietnam War. It was almost silent, except for the clipping of Park Police horse hooves on gravel, the rustling of the leaves and the faint strains of the national anthem played in the distance.

The people who gathered — veterans, parents in uniform with their children, runners who paused midstride — were there not just to pay respects to Mr. McCain. They were there for Ms. McCain and their own loved ones who had served.

“Makes us feel special at a very hard time for all of us,” said Bruce Whiteaker, 69, who served in the Air Force during the Vietnam War. “We’re grateful that she’s decided to stop and honor the fallen in this way.”

Mr. Whiteaker made the 10-hour drive from Knoxville, Tenn., with his wife, Shirley, who also served in the Air Force. They brought handmade signs, decorated with American flag stickers, and condolences for the McCain family.

“With Cindy McCain coming today,” Ms. Whiteaker said, tears beginning to run down her face, “we wanted her to know what we felt for her and her family.”

Onlookers ponder ‘what it means to be great.’

A stubborn grayness rested over Washington, the vast sheet of dark clouds threatening rain as clusters of mourners walked into the cathedral, dressed in black. An American flag hung at half-staff on the front lawn.