Speaking to reporters in the White House briefing room, Sanders was asked if Trump's pledged money would come from his personal finances or another source, such as a private charitable foundation he founded or his real estate company.
Before taking office, Trump, a real estate baron and television personality, had a history of overstating his charitable giving and taking credit for donations that came from other sources, as documented in a series of stories past year in The Washington Post.
Trump has had a spotty record when it comes to pledging and then actually carrying through on his promises to donate money to charities.
"He'll pledge probably $1 million of his own personal money to help the people of both Texas and Louisiana", said Sanders. Sanders couldn't say on Tuesday afternoon or Wednesday whether the President had yet donated funds himself, saying only that he was looking into it.More news: Lebanese Army Declares Cease-Fire with IS on Syrian Border
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Trump used a similar "reporters decide" gimmick at the beginning of his administration, that time with his presidential salary, which he is declining to accept. Then-press secretary Sean Spicer told reporters at a March briefing that Trump "has kindly asked you all determine where that goes". He gave his first installment to the National Park Service and his second to the Department of Education.
"I mean, I've heard $100 billion bantered around - not for a vote next week - but that may be the total amount of some kind of emergency package when it's all said and done".
President Trump visited Texas, where Hurricane Harvey has caused historic devastation in the one week since the epic rainfalls.
Vice President Pence surveyed flooded-out areas of Texas on Thursday.