Senators voted Wednesday to approve an amendment to the bipartisan immigration bill that would bolster security along the U.S.-Mexico border.

Sen. Lamar Alexander (R-Tenn.), one of 15 GOP senators who voted to approve a border security amendment. (Mark Humphrey/AP)

The agreement would require the U.S. Border Patrol to double in size and deploy roughly 40,000 agents along the southern border. The Department of Homeland Security also would need to complete construction of 700 miles of fencing and deploy radar and unmanned aerial drones in the region to track illegal border crossings.

The bipartisan "Gang of Eight" who wrote the immigration bill under consideration agreed to the changes in hopes of securing as many as 70 votes on final passage of the bill, which is expected later this week.

On this vote, to approve the amendment, supporters fell just short of the 70-vote goal. Here's a breakdown of the vote:

Final tally: 69 to 29.

All 54 members of the Senate Democratic caucus voted for the amendment as well as 15 Senate Republicans. Every member of the "Gang of Eight" voted in favor of the amendment.

Democratic "yes" votes: All 54 members of their caucus, including Gang of Eight members Michael Bennet (Colo.), Richard Durbin (Ill.), Robert Menendez (N.J.) and Charles E. Schumer (N.Y.).

Republican "yes" votes: Sens. Lamar Alexander (Tenn.), Kelly Ayotte (N.H.), Jeff Chiesa (N.J.), Susan Collins (Maine), Bob Corker (Tenn.), Jeff Flake (Ariz.), Lindsey O. Graham (S.C.), Orrin G. Hatch (Utah), Dean Heller (Nev.), John Hoeven (N.D.), Mark Kirk (Ill.), John McCain (Ariz.), Lisa Murkowski (Alaska), Marco Rubio (Fla.), Roger Wicker (Miss.). Flake, Graham, McCain and Rubio are the GOP members of the gang.

Republican "no" votes: 29 senators, including Senate Minority Leader Mitch McConnell (R-Ky.) and his deputy, Sen. John Cornyn (R-Tex.).

Who didn't vote?: Roy Blunt (R-Mo.) and Mike Lee (R-Utah).

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