Updated

The U.S. Senate unanimously voted in favor of an amendment Wednesday that guarantees zero funding for programs that include the transfer of firearms to drug cartels unless law enforcement continuously monitors the weapons "at all times."

The amendment stemmed directly from Operation Fast and Furious, the controversial botched weapons program, and was introduced by Sen. John Cornyn, R-Texas.

The amendment passed 99-0, with only Sen. Kent Conrad, D-N.D., missing the vote.

During floor debate on Tuesday, Commerce, Justice, Science Appropriations Subcommittee Chairwoman Barbara Mikulski, D-Md., jumped on board and praised Cornyn's effort to prevent any more programs like the botched "gun-walking" effort that enabled U.S.-purchased weapons to end up in the hands of Mexican drug cartels.

In a rare show of bipartisanship, Mikulski not only commended the Texas Republican, but said she would join with him in getting answers from the Justice Department about what officials at the top knew about the program and when.

"When I look at what happened in Operation Fast and Furious, I was fast to be furious," Mikulski said, faulting flawed leadership and questionable intelligence for the "bungled" and "botched" program.

As news reports reveal similar past operations to Fast and Furious, Cornyn's amendment would ban Justice Department appropriations to be used for "the knowing transfer of firearms to agents of drug cartels where law enforcement personnel of the United States do not continuously monitor or control such firearms at all times."

Asked how the term "agents" would be defined, an aide said the term is "self-explanatory."

The amendment, which would be part of a "minibus" appropriations bill for fiscal year 2012 that contains Mikulski's jurisdiction as well as agriculture, transportation and housing spending, could be approved as early as Tuesday.

The vote comes as the Department of Justice as well as the Bureau of Alcohol, Tobacco, Firearms and Explosives is under scrutiny for Operation Fast and Furious, which Sen. Chuck Grassley, R-Iowa, a key congressional investigator, said Tuesday "went critically wrong."

"By March of 2010, the ATF had gathered evidence that the intent of the straw buyers was to transfer these weapons to criminals and Mexican drug cartels," Grassley told an audience at Judicial Watch, which has been petitioning the government to release documents on the operation.

Noting that rather than shutting it down, Grassley said the operation continued with false assurances to gun dealers that the suspects would be stopped before damage was done.

Instead, the operation wasn't brought to an end until U.S. Border Patrol Agent Brian Terry was killed on Dec. 15, 2010.

"Two of the weapons bought right under the ATF's nose nearly a year earlier turned up at the murder scene," Grassley noted.

But an attorney representing one of the ATF officials at the center of this storm sees it differently, insisting the description that the guns were allowed to "walk" is not fair. He describes the ATF behavior in this case as "not an unusual strategy, it's a typical strategy. It does not involve allowing guns to walk."

Saying that the investigation is not all about politics, but about making sure "nothing like this ever happens again," Grassley criticized Attorney General Eric Holder for claiming he was in the dark over the program despite receiving several memos about the program.

Holder has suggested he didn't read the memos, and wasn't made aware of the operation's failings until April 2011. Grassley says Holder should have known early on because his No. 2 had been briefed on the operation back in March 2010.