"Now he's moved himself to an incomplete, because the truth is we don't know what his tax plan is anymore. The old plan is off the website, so it's gone," the former chief economist of the president's Council of Economic Advisers under George W. Bush said.
In one of the few new details announced on Monday, Trump raised his proposed top income tax bracket to 33 percent, up from 25 percent.
Trump's adoption of tax brackets devised by a Republican House task force is a step in the right direction, Holtz-Eakin said, but it remains to be seen how much of the overall plan he will adopt.
"There's a sense of incompleteness," he said.
Holtz-Eakin said he was unable to calculate a cost for the tax plan, but praised the campaign's commitment to make it revenue-neutral. Analysis of the previous tax plan put its cost at $10 trillion, a figure Holtz-Eakin said is "unthinkably large."
As for Trump's promise to make child-care expenses deductible, Holtz-Eakin said it was "a weird way to go" because few Americans would qualify for it. Essentially, it amounts to a bigger personal exemption for every child deducted for those families that do qualify, he said.
"This drives Republicans crazy, because he's campaigning like a Democrat. Democrats say, OK, here are target constituencies. Let's give them something and see if we can win," he said.
Trump extended an olive branch to the Republican establishment — a tax refund to female voters, with whom he is currently unfavorable — and offered an anti-trade message and promises of infrastructure spending to blue-collar workers, Holtz-Eakin said.