A 2014 VA department investigation into the death of veterans found severe issues with record keeping which contributed to their deaths.
Trump was refering to the scandal which hit the Department of Veterans Affairs in 2014. Officials at the Phoenix VA hospital were accused of maintaining a secret wait list of veterans seeking health care. This list was kept out of sight of federal regulators, who were instead sent documents that vastly underreported how long it took for patients in Phoenix to see a doctor. It was found that patients had to wait an average of 115 days to be seen by a primary care provider. Those long wait times may have had dire consequences, CNN reported, and as many as 40 veterans died while on waitlists at the Phoenix hospital. An official investigation found the wait time contributed to their death.
After news of the scandal broke, lawmakers asked the inspector general to investigate the scale of the VA application backlog and the deaths that resulted. Investigators found that the VA data system was in chaos. In 2014, the database contained applications for people who died before 1998. In the course of moving millions of records around in 2013, the VA inadvertently created enrollment entries for people "who never sought care or applied for enrollment." The database also included anyone who had any contact with the VA.
The report made it clear that data limitations prevented the investigators from determining exactly how many patients applied for appointments or when. The inspector general was able to match Social Security death records with over 307,000 applications listed as pending, but that included people who might never have applied or been eligible for care, which means that Trump's figure was inaccurate.