Gary Cohn, the former head of the National Economic Council and key advisor to President Donald Trump, said personal tax cuts need to be made permanent.
In his first interview since exiting the White House, Cohn said that is the one piece of unfinished business he left behind. Cohn announced his resignation in March and left in early April.
"The one thing that we regret not having been able to do in the original tax bill was the personal side expired. We would like to go back and make the personal side permanent," Cohn told CNBC's Bib Pisani in a "Squawk on the Street" interview. "We do not want that to expire."
The original tax bill, which Congress passed in December, slashed corporate taxes from 35 percent to 21 percent and reduced tax rates for millions of Americans. It also doubled the standard deduction.
Cohn endorsed an idea by House Ways and Means Chairman Kevin Brady to do a "tax cut 2.0" bill that would continue to review the current tax system — and make the changes to the personal tax reforms permanent.
"Chairman Brady has an interesting idea and it's something that we should do. He thinks we should do tax modifications every year," he said. "The world's always changing, tax law's changing. We in the United States should not stay stagnant."
Critics of the tax bill say it was skewed toward the rich and will blow a hole in the budget and pile onto the $21 trillion current debt load.
The deficit stands at $382 billion for the first seven months of the fiscal year, through April, according to the Congressional Budget Office. That's 10.7 percent higher than the same period for the last fiscal year.
However, April was the best surplus month in U.S. history, with receipts outpacing expenditures by $218 billion. That easily beat the previous surplus record in April 2001 of just shy of $190 billion.
Cohn said the tax bill was "the big accomplishment" of his time in the Trump administration.
He was succeeded in his job by former CNBC journalist Larry Kudlow.
The interview came during the BTIG Charity Day, during which the brokerage raises donations for multiple charities, many focused on children.