In one high-profile example a year ago, he failed to give a promised $1 million of his own money - plus another $5 million he said he'd raised - to veterans' organizations until reporters asked questions months later about who had received the charity.
Most of the money - about $5.5 billion - will go directly to FEMA's disaster relief efforts.
The formal request came late Friday in a letter from President Donald Trump's budget chief to House Speaker Paul Ryan.
The president reportedly has yet to decide which organizations will receive the donation, which will come from his personal fortune.
Asked later in the day about the claim, Sanders said he had talked with state and local officials who "are eating, sleeping, breathing the Harvey disaster". The White House can say Trump made a well-intentioned mistake in his description, but changing the meaning of words shouldn't be one of the press secretary's options.More news: Late Goal Glut Saves England's Blushes After Mediocre Display Against Malta
Trump has pledged damaged areas will get all the help they need from his administration.
Sources on the Hill increasingly believe Trump is leaning toward ending renewals and new applicants to the program, and a source familiar has said the White House is considering that option.
He also says no routine sweeps will be conducted in emergency shelters.
Bossert didn't expand on what types of long-term assistance people in the country illegally would be able to obtain, but said some types of assistance may be open only to citizens.
"I think we have every reason to believe that that's going to happen in a responsible way", he said.
Some 195,000 people have registered with the US government for financial assistance due to massive flooding in Texas caused by Tropical Storm Harvey, the Federal Emergency Management Agency said on Wednesday.