Mr Trump told reporters in the White House that they should ask him again “in a number of weeks from now.”
“They should be looking at all of this fraud,” said Mr Trump.
“This is not civil, he thought it was civil. This is not civil, this is criminal stuff. This is very bad criminal stuff.”
Mr Trump is still considering if he should fire the attorney general over the comments, according to NBC News.
The outgoing president has refused to concede the election to Joe Biden and has repeatedly made false claims of voter fraud.
But his legal team has shown no evidence to back up his claims and has been repeatedly defeated in courtrooms in states across the country.
Mr Trump made his comments in the Oval Office as he presented former Notre Dame football coach Lou Holtz with the Presidential Medal of Freedom.
Mr Holtz, 83, is a vocal supporter of Mr Trump and spoke for him at the Republican National Convention in August.
During his speech he controversially called Mr Biden “a Catholic in name only” which earned him admonishment from the president of Notre Dame.
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