The Senate on Monday advanced the nomination of Justin Muzinich, a key designer of the administration's tax overhaul, to be deputy secretary of the Treasury.

Muzinich, a veteran of Wall Street, has served as a top aide to Treasury Secretary Steve Mnuchin for more than a year. The Senate voted 55-43 to invoke cloture, allowing for a final vote on the nomination midweek.

Democrats angered over Trump's tax policy held up Muzinich's nomination for months, following a party-line 14-13 Senate Finance Committee vote in July. Sen. Ron Wyden, D-Ore., who placed the hold on the vote, was still fuming about the nomination on the Senate floor Monday. "If a Treasury nominee says that the Trump handouts will pay for themselves, I intend to oppose them," the senator said, calling the claim the "economic policy version of being a flat Earther."

The deputy secretary position has been empty since Mnuchin was confirmed last year. President Trump’s previous nominee, Goldman Sachs executive James Donovan, withdrew from consideration last year. Republicans argued the hold-up was undermining the department's ability to do its job properly.

"As the Treasury Department continues its work implementing the new tax code ... it is more important than ever that the deputy secretary position be filled," said Senate Majority Leader Mitch McConnell, R-Ky.

Muzinich, 40, is a Harvard M.B.A. and Yale-educated lawyer and has been viewed as a centrist voice inside the department. On Wall Street, he worked as a banker at Morgan Stanley and as the president of Muzinich & Company, an investment firm and family business founded by his father. He has been serving in the Treasury Department since February 2017 as counselor to the Treasury secretary, a position that doesn't require Senate confirmation.