Ms. Dunn’s new role was greeted enthusiastically by some on Mr. Biden’s staff who have been frustrated by the bickering and view her as a unifying and respected figure across generational lines.

But in a sign of the tensions on the campaign, and the growth of rival factions who are and are not loyal to Mr. Schultz, other Biden officials sought to downplay the elevation of an already-senior official, suggesting it was mostly done to reassure the vice-president himself.

The move follows days of speculation inside Mr. Biden’s Philadelphia headquarters about potential staff shake-ups following a disappointing Iowa result that has complicated Mr. Biden’s path forward. Before her elevation, Ms. Dunn had been focused chiefly on communications strategy.

Her new leadership role, which came with Mr. Biden’s blessing, signals that the campaign recognizes a need to make changes. But it’s not clear that promoting Ms. Dunn will alter Mr. Biden’s trajectory in the race — or be the last change Mr. Biden makes.

A spokesman for the Biden campaign, T.J. Ducklo, declined to comment.

Ms. Dunn, a managing director at the public affairs firm SKDKnickerbocker, is a longtime Democratic strategist who has worked on a number of presidential campaigns and grew close to Mr. Biden when she worked in the Obama White House. She has been dividing her time between Washington, the Philadelphia headquarters and on the campaign trail with Mr. Biden.