Mr. Buttigieg’s supporters, though, are somewhat irked by the scrutiny.

In an email Monday to would-be contributors, one Washington-based Democratic consultant who has been helping the mayor raise money characterized the McKinsey questions as the product of opposition research.

“And yes, the opposition-placed stories about McKinsey are predictable but no less important to address,” wrote the consultant, Alex Slater, in the email under a header “McKINSEY MADNESS.” “I’m sending a link to Pete’s statement released on his work at McKinsey as well as a timeline of summary of the work that he performed at the firm.”

Mr. Buttigieg and Ms. Warren for weeks have been engaged in a bitter campaign for Democratic support in Iowa, a state both of their campaigns view as critical to their path to the presidential nomination.

Their sparring over transparency escalated shortly before Thanksgiving, when Mr. Buttigieg challenged Ms. Warren to release tax returns from beyond the 11 years she had already made public, while releasing his own tax returns from the three years he worked at McKinsey. Those tax returns revealed no details about the type of work he did for McKinsey, only the locations of the offices to which he was assigned.

Over the weekend Ms. Warren renewed calls for Mr. Buttigieg to open his fund-raisers and name his campaign’s bundlers, telling reporters in New Hampshire that she was concerned about “conflicts being created every single day when candidates for president sell access to their time to the highest bidder.”

Mr. Buttigieg’s concession on his donors and the release of his McKinsey work comes on the heels of Ms. Warren’s decision Sunday to detail how much money she made from her corporate work. Their dueling disclosures suggest that both candidates believe they can defuse criticism — and effectively end the other’s main line of attack — by putting out information that may be somewhat unflattering.

In Las Vegas Monday night Ms. Warren said she was “glad to see what the mayor has done,’’ but that to win the White House “we have the candidate who can most aggressively make the comparison between Trump’s administration and how Trump has raised money, and how the Democrats are going to do it.”