WASHINGTON (CN) - President Barack Obama vetoed a defense-spending authorization bill that the administration says circumvents spending caps.
The Senate originally passed the bill in June, but made changes that required the bill to go to conference. The Senate sent the bill to the president on Oct. 7.
Democrats in the Senate criticized the bill for skirting the Budget Control Act by sending money into the uncapped Overseas Contingency Operations "slush fund." The White House echoed these concerns leading up to the Senate's passage of the bill.
"Specifically, the bill's use of $38 billion in Overseas Contingency Operations funding - which was meant to fund wars and is not subject to budget caps - does not provide the stable, multi-year budget upon which sound defense planning depends," Obama wrote in the veto message accompanying the bill to the House of Representatives.
Sen. John McCain, R-Ariz., was a vocal supporter of the bill during the fight over its passage. When Obama's veto of the legislation was still just a threat, McCain, who heads the Senate Committee on Armed Services, called the move "shameful and "nonsensical."
Senate Majority Leader Mitch McConnell, R-Ky., echoed that sentiment on the Senate floor Thursday.
"This is the worst possible time for an American President to veto their national defense bill, and especially to do so for arbitrary partisan reasons," McConnell said. "Republicans and Democrats here in Congress who worked so hard to pass this important legislation - legislation that authorizes the exact amount the Commander-in-Chief requested - must now work together again, this time to override the President's partisan veto."
Congress could override the veto with a two-thirds majority vote in both houses, but it would be a tough task. Congress has managed to override just more than 6 percent of presidential vetoes since World War II, according to data on the U.S. Senate website.
To override the veto, House Republicans would need to scrounge up 20 votes, requiring them to convince at least seven Democrats who originally voted against the conference report or abstained to support the veto override. Senate Democrats could block the veto by getting just four of the 21 Democrats who voted against the bill the first time around to come back on board.
The veto is Obama's fifth of his term and the third this year. He also vetoed the National Labor Relations Board Union Election Rule and the Keystone XL Pipeline Approval Act earlier this year, according to the U.S. Senate website.
Vetoes have been a less-commonly used tool for presidents in recent years, with the rise of divided government and the effectiveness of even the threat of a veto making it less necessary, Brandon Rottinghaus, associate professor at the University of Houston Department of Political Science said in an interview.
"The last thing Congress wants to do is work on legislation for several months only to have it decimated by the president," Rottinghaus said.
Presidential vetoes of defense-spending or authorization bills specifically are somewhat rare, because presidents typically get what they want with this type of legislation, Rottinghaus said.
President George W. Bush vetoed a defense-appropriations bill in 2007 in protest of a provision in the law that mandated a drawdown in forces in Iraq.
It isn't a coincidence both vetoes occurred late in the second term of a presidency and involved issues that defined both men's time in office - the war in Iraq for Bush and the fight over the budget for Obama, Rottinghaus said.