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The Senate cleared a key procedural hurdle Wednesday on the judicial nomination of David Barron, the former Justice Department lawyer who authored memos providing legal justification for using drone strikes against U.S. citizens.

The Senate voted 52-43 to invoke cloture on Barron's nomination to the 1st Circuit Court of Appeals. Barron is a Harvard Law professor and formerly worked in the Obama administration as an acting assistant attorney general in the Office of Legal Counsel, where he penned the drone memos.

Barron's nomination became controversial as senators took issue with the substance of the drone memos and the fact they had not been released to the public. The Obama administration has agreed to make one of the redacted memos about drone strikes publicly available, a move that swayed some Democrats who considered opposing Barron's nomination, including Sen. Mark Udall, D-Colo. Senators had the opportunity to view the classified memos ahead of the vote.

Sen. Rand Paul, R-Ky., a fierce critic of the Obama administration's drone policy, took to the floor for 31 minutes Wednesday morning for a filibuster-type speech protesting Barron's nomination.

"I rise today in opposition to the killing of American citizens without trial. I rise today to oppose the nomination of anyone who would argue the president has the power to kill an American citizen not involved in combat and without a trial," Paul said.

"It isn't just about seeing the Barron memos," he said. "I believe it's about what the memos themselves say. I believe the Barron memos at their very core disrespect the Bill of Rights."

Paul asked to delay a vote on Barron's nomination until the American public had the opportunity to read the memo, but his request was objected to. Last year, Paul launched a 13-hour filibuster related to the nomination of John Brennan to be CIA director, demanding that the White House explain its justification for the use of drones against U.S. citizens.

Two Democrats joined Republicans in voting against Barron's nomination - Sen. Mary Landrieu, D-La., who is up for re-election this year, and Sen. Joe Manchin, D-W.Va. Sens. Kelly Ayotte, R-N.H., John Boozman, R-Ark., Dan Coats, R-Ind., Marco Rubio, R-Fla., and Jeanne Shaheen, D-N.H., did not vote.

A final confirmation vote on Barron's nomination was slated for 2 p.m. Thursday.

This post was updated. A previous entry incorrectly said Sen. Richard Shelby, R-Ala., did not vote, but he did cast a vote in opposition to Barron.