ORLANDO, Fla. — Of all the attacks that Hillary Clinton and her fellow Democrats have tried against Donald J. Trump since he captured the Republican presidential nomination, one has stood out for its emotional force and persuasive power: No one, it seems, can abide Mr. Trump’s mockery last year of a reporter’s physical disability.

And as Mrs. Clinton strains to make a more affirmative case for her own candidacy, after a summer focused largely on hammering Mr. Trump, her campaign believes that a focus on an often-overlooked constituency — voters with disabilities — can accomplish both goals at once.

On Wednesday, without mentioning the Trump episode, Mrs. Clinton discussed her vision for an “inclusive economy” with expanded job opportunities for what she called “a group of Americans who are, too often, invisible, overlooked and undervalued — who have so much to offer, but are given far too few chances to prove it.

“That’s been true for a long time,” she said, “and we have to change it.”

In keeping with a recent campaign theme, she described how her career had informed her policy goals, from her work for people with disabilities during her time at the Children’s Defense Fund to her tenure as secretary of state, when she appointed the first special adviser for international disability rights.