The Senate easily approved a waiver for retired Gen. James Mattis on Thursday that paves the way for him to serve as President-elect Donald Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE's Defense secretary.

Senators voted 81-17 on the waiver, which will allow the former general to bypass a law that requires Pentagon chiefs to have been out of uniform for seven years.

Mattis retired from the military in 2013.

The House is expected to vote on the waiver on Friday.

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The vote came within hours of the Senate Armed Services Committee approving the waiver, with only three committee Democrats voting against it.

Sen. John McCain John Sidney McCainKelly's lead widens to 10 points in Arizona Senate race: poll COVID response shows a way forward on private gun sale checks Trump pulls into must-win Arizona trailing in polls MORE (R-Ariz.) touted Mattis's bipartisan support ahead of the vote.

"Many of us have known him for years and years as he has shown the outstanding characteristics of leadership that he has had the opportunity in service to this country," he said.

Democrats initially resisted tying the waiver to a Senate spending bill late last year, but opposition quickly fizzled after lawmakers reached a deal to simply expedite the process while maintaining a 60-vote threshold.

Sen. Jeff Merkley Jeffrey (Jeff) Alan MerkleyThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Sunday shows - Trump team defends coronavirus response Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (D-Ore.), who voted against the waiver, warned that lifting the rule for Mattis makes it easier to do so in the future for another nominee.

"I stand on the side of maintaining the principle of civilian control," he said. "Each time we violate this principle it's easier next time to say it's been done before."