At a rally in Grand Rapids, Mich., on Wednesday evening, John Edwards endorsed Barack Obama, who was on the stage with him, to be the Democratic nominee for president.

Sounding a theme of a nation divided into parts by walls, Mr. Edwards said, “The reason I am here tonight is that Democratic voters in America have made their choice and so have I.”

Mr. Edwards then went on to say, “There is one man who knows in his heart that it is time to tear down that wall and make one America, Barack Obama.”

Mr. Edwards has carefully played down his aspirations for an administration role. In an interview in January, he said he would not accept a vice-presidential spot or Cabinet position. “No, absolutely not,” he said, shaking his head emphatically when asked.

But privately, he told aides that he would consider the role of vice president, and favored the position of attorney general, which would appeal to his experience of decades spent in courtrooms as a trial lawyer in North Carolina; and his desire to follow in the footsteps of Robert F. Kennedy, one of his heroes.

The endorsement comes at a time when the appeal of Mr. Obama appears to be lagging among white, blue-collar voters, a group to which Mr. Edwards openly appealed.