President-elect Joe Biden's nominee for secretary of defense, retired Gen. Lloyd Austin, will sit for his confirmation hearing before the Senate Armed Services Committee on Tuesday, but he will have to clear one more hurdle in order to get the job – a waiver that allows recently retired military service members to lead the Defense Department.

Current law requires a civilian to serve as defense secretary – meaning that a nominee who has served must have retired at least seven years prior to holding the office, unless Congress agrees to a waiver of that requirement. A number of Democrats have indicated they will agree to such a waiver, even though they opposed doing the same for President Trump's first defense secretary, Gen. James Mattis.

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"The internal security threat the U.S. faces right now is serious. We need a Secretary of Defense on the job immediately," Sen. Chris Murphy, D-Conn., tweeted Monday. "I will vote to confirm Lloyd Austin and grant him a waiver, and I urge other Senators to do the same.

Murphy acknowledged that he opposed a waiver for Mattis and defended the change in stance by claiming that confirming Austin swiftly was necessary due to "internal security" threats.

Murphy also claimed that a waiver for Mattis was problematic for him because President Trump and his then-incoming Secretary of State Rex Tillerson lacked experience, and he did not trust National Security Adviser Michael Flynn.

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"A general at DoD was especially worrying under Trump," Murphy said. "Trump had zero foreign policy experience, a penchant to glorify violence, a total neophyte Secretary of State, and an unstable, war mongering former general as NSA."

Murphy went on to claim that the situation is now "different" under Biden, due to his extensive government experience and the diplomatic experience of several of his Cabinet picks.

The Connecticut senator was not the only one who opposed a waiver for Mattis but is now publicly supporting one for Austin. House Armed Services Committee Chairman Rep. Adam Smith, D-Wash., also feels differently about the current situation.

"Today I sent a letter to all my Democratic colleagues in the House, urging them to vote in favor of granting Secretary of Defense designate @LloydAustin the waiver necessary to complete his historic confirmation," Smith tweeted.

Smith's opposition to Mattis's waiver, however, was largely due to its broad nature – it did not specifically name Mattis – and the fact that Mattis did not sit for a hearing on the issue.

"If we don't stand up for ourselves now, we're going to be rolled over countlessly," Smith said at the time, according to Politico.

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"We all want to support Gen. Mattis. We want that bipartisan vote," he continued. "The way to get that vote is to do what we said we were going to do and have him come before the Armed Services Committee."

Austin is scheduled to appear before Smith's committee on Thursday.