Many economists have questioned whether Mnuchin's target of 3 percent growth is achievable and sustainable, given the shrinking of the U.S. labor force. And even if the economy does speed up, it's unclear that 3 percent growth would be enough to pay for the dramatic reductions in corporate and personal tax rates proposed by Trump during the campaign, or by House Republicans since the election.
Trump repeatedly suggested before the election that growth could hit as much as 6 percent. His campaign's own analysis of his economic proposals assumed that growth would reach 4 percent. Mnuchin walked back that number in an interview with CNBC in November, shortly after his nomination, citing 3 to 4 percent growth.
On Thursday, Mnuchin promised only 3 percent growth or higher.
Republicans have been hoping to pass tax reform using the budget reconciliation process, which would only require only a simple majority of senators to approve it. However, that also means the tax cuts would not be able to add to the deficit in the long term.
A conservative analysis by the Tax Foundation of the plan Trump proposed during the campaign estimated it would cost $2.6 trillion over the next decade, even after accounting for improved economic growth. A dynamic evaluation by the Tax Policy Center projected the price tag would hit $21 trillion by 2036.
"There's a big difference between dynamic scoring and directed scoring," said Jason Furman, a senior fellow at the Peterson Institute for International Economics who was former President Obama's chief economist. "They started with a growth rate and asserted they could achieve it."