For Mr. Walker, who is fond of joking that “Madison is 68 square miles surrounded by reality” – a rendering of a quote first used by former Gov. Lee S. Dreyfus, the scene on Monday afternoon in the state’s capital must have seemed surreal.

As dozens of teachers and other public employee union members with whom Mr. Walker has often clashed cheered in the bright sunshine outside the Edgewater Hotel, a few blocks from the State Capitol, Walker entered a small, windowless room in the hotel’s lower level, where about 70 reporters and photographers were waiting. In that room, with drab gray walls, at a podium hastily placed in front of an American flag and the Wisconsin flag, the 47-year-old governor read a terse speech announcing that he was suspending his campaign.

Mr. Walker took the podium alone. His son Alex stood in a doorway, but Mr. Walker’s wife, Tonette, and their son Matt were nowhere in sight.

Mr. Walker quickly turned after finishing his statement and exited a side door to shouts from the news media.

Seventy-one days earlier, Mr. Walker had announced his entry into the 2016 race before thousands of wildly cheering supporters in a pavilion at the Waukesha County Fairgrounds, where speakers blared “Only in America” and a giant backdrop displayed his last name with a stylized American flag replacing the letter “e.” Matt and Alex were M.C.s then, and Mrs. Walker spoke proudly of her husband’s ability to “fight and win.”