Senators voted 32-68 on overriding a "point of order" placed on the amendment by Sen.(I-Vt.). Sixty votes were need to overcome the procedural hurdle.

The amendment, offered by Sens.(R-Ark.) and(R-Fla.) divided Senate Republicans, including potential 2016 presidential candidates. Rubio and Sen.(R-Texas), who launched his presidential bid earlier this week, supported the amendment, while Sen.(R-Ky.) voted against it.

The amendment would have swapped out the fiscal 2016 defense budget numbers with projected numbers included in former Defense Secretary Robert Gates's fiscal 2012 defense budget.

"This is a pretty simple amendment, it funds defense fully," Rubio said ahead of the vote. "It puts us at the Gates budget number ... that fully funds the needs of our military."

Sanders slammed the Republicans' amendment, calling it "remarkable."

"This is truly a remarkable amendment because it runs directly in opposition to what the Republicans have been talking about," Sanders said, referring to Republicans' pledge to balance the budget and shrink the deficit. "Enough is enough, if you want to go to war, start paying for it."

The Pentagon's 2012 budget projected the department would need $661 billion in fiscal 2016, according to a summary of the budget released by the department