The most severe problem is the scandal over falsified waiting lists that last month led to the ouster of the department’s top two officials, including Mr. Shinseki. He had characterized the lack of honesty and proper behavior at some of the department’s facilities as a “systemic, totally unacceptable lack of integrity” that he could not explain.

The waiting-list controversy revealed that veterans in many places faced long delays for appointments — delays that were hidden by administrators and scheduling employees who were under pressure to convince their bosses that waits were typically no longer than 14 days. Results of investigations and audits in recent weeks have suggested that the cover-ups of the delays were spurred in many places by administrators whose performance ratings were tied to measurements of how long it took veterans to see doctors.

Veterans Affairs officials have already taken steps to eliminate what they now acknowledge were potentially perverse incentives to manipulate waiting-time data, such as eliminating performance bonuses this year for senior health care executives and deleting the 14-day goal from employee contracts.

But the underlying cause of the delays will be harder to address: The department’s medical centers and clinics have seen a sharp increase in visits scheduled by patients, particularly for primary care appointments, but the number of doctors and nurse practitioners available to see them has in many places barely grown.

Much of the demand has come from younger veterans of Iraq and Afghanistan with profound and complex injuries that require close monitoring and many follow-up visits. But most veterans seeking treatment at department clinics, though, are Vietnam veterans, many with chronic illnesses like diabetes that require long-term care, or with cancer or cardiovascular disease, which require complicated and expensive treatments.

In addition, if confirmed, Mr. McDonald will be confronted with the continuing problem of how to make sure veterans returning from the battlefield, some of them seriously injured or battling psychological problems, receive their disability compensation in a timely manner. In his 2008 campaign, Mr. Obama criticized delays in providing benefits to veterans and promised to make fixing the agency a top priority. But while the White House has bragged about making progress in the timely distribution of benefits, the revelations this spring about delays in seeing patients has raised the agency’s profile to a new political level.

To win confirmation, Mr. McDonald will have to win over lawmakers in both parties. Records show that Mr. McDonald has made political contributions only to Republicans, giving $5,000 to Mitt Romney, the Republican presidential nominee in 2012, and $11,000 to the Romney Victory Committee. He has also made several contributions to Speaker John A. Boehner and Senator Rob Portman, both Republicans of Ohio.