Gov. Bob McDonnell (R-Va.) has long been on almost everyone’s short list for the Republican vice presidential nomination. But the recent controversy over Virginia’s law requiring ultrasounds before abortions may have hurt McDonnell’s chances at the VP nod (he somehow managed to anger social conservatives by backing a watered-down version of the bill and moderates who say the fight plays right into Obama’s “war on women” strategy). Still, McDonnell enjoys 62 percent approval in a swing state that is critical to the GOP’s prospects this November. And as a 21-year Army veteran, and the father of a daughter who served as a platoon leader in Iraq, he seemed to bring strong national security credentials to the GOP ticket.

But now McDonnell’s national security credentials have come into question, thanks to his mishandling of a bill passed by the Virginia General Assembly that disassociates the commonwealth from the military detention of al-Qaeda or its terrorist affiliates who happen to be U.S. citizens. The bill, HB 1160, would effectively bar Virginia state troopers from arresting a terrorist like Anwar al-Awlaki if they knew he would be put in military detention. McDonnell didn’t raise a finger to stop this odious legislation as it made its way through the Virginia legislature. As a result, it passed 97-3 in the House of Delegates and 39-1 in the state Senate.

Far from fighting this bill, McDonnell’s office issued a statement on passage expressing the governor’s “shared concern that Virginia does not participate in the unconstitutional detention of U.S. citizens.” Of course, there have been no “unconstitutional detentions of U.S. citizens” — but instead of pointing this out and opposing the statute, McDonnell gave credence to the false premise that underpins it.

Former attorney general Ed Meese and former Homeland Security secretary Mike Chertoff wrote McDonnell detailing HB 1160’s many practical dangers and constitutional flaws, and told him, “We strongly urge you to veto the bill.” The governor rejected their advice. McDonnell spokesman Tucker Martin told me the governor believes “that terrorist acts against our nation by enemy groups and combatants should be dealt with for what they are — acts of war,” and that an American citizen can be held as an enemy combatant, provided he can challenge his detention in court. But once the bill had been approved by such overwhelming margins, his office says, McDonnell had only three options: veto it (and see his veto overridden) sign it, or amend it. He decided to go along with the bill and amend it with provisions to protect Virginia’s ability cooperate in law enforcement efforts in the war on terror.

Conservative experts in national security law, including former Justice Department official David Rivkin and Charles “Cully” Stimson, a former deputy assistant secretary for detainee affairs at the Defense Department, say that McDonnell’s amendments do little to mitigate the impact of the legislation. But the bigger question is: Why did the governor wait until the bill had passed by veto-proof majorities to do something about it? Surely a politician as persuasive as McDonnell could have lobbied legislators behind closed doors, explaining why the bill was dangerous and unconstitutional, and why it should be defeated. But McDonnell didn’t try and fail to stop the bill — he failed to even try.

McDonnell’s failure will have national implications. Virginia is not just any state. It is home to the Pentagon, the CIA, the FBI training center at Quantico and a number of major military bases. If a bill like HB 1160 can pass in Virginia, why shouldn’t the 13 other states now considering similar legislation follow suit?

And McDonnell’s failure could also have implications for his vice presidential aspirations. The Wall Street Journal wrote recently that his “rollover [on the detainee bill] hardly speaks well of Mr. McDonnell’s bona fides as a potential vice president.” After all, if McDonnell were elected on the GOP ticket with Mitt Romney, he would serve as president of the Senate. Would this be his approach in Washington when some senator proposes similarly egregious legislation — to say nothing and wait on the sidelines until the legislation gains a veto-proof majority?

Compare McDonnell’s inaction to last week’s fight over terrorist detention legislation on Capitol Hill. When Reps. Adam Smith (D-Wash.) and Justin Amash (R-Mich.) offered an amendment that would have barred military detention for al-Qaeda terrorists captured in the United States, Republican leaders rallied the GOP caucus to defeat the amendment. Thanks to their efforts, only 19 Republicans voted in favor. By contrast, all but four of the 87 elected Republicans in Richmond voted to have the state employees of Virginia lay down their arms in the war against al-Qaeda. That is a failure of leadership. It is also a serious blow to McDonnell’s chances of becoming the next vice president of the United States.