This vote was on an amendment by David Vitter, R-La., that would require the full implementation of the US-VISIT system be included as one of the underlying bill's "enforcement triggers." In essence, this would require that the US-VISIT system be fully implemented before certain provisions in the underlying bill could be put into effect.

US-VISIT gathers fingerprint scans and a digital photograph from everyone who applies for a visa. The aim is to prevent known terrorists and criminals from entering the country. The "entry" portion of US-VISIT – scrutinizing biometric data at the point of entry into the United States – is finished. But the "exit" portion – which would help identify people who overstay their visas – is not finished.

The amendment was offered to a measure that is intended to overhaul the nation's immigration system. The bill represents a hard-won compromise between competing sides of the immigration debate: those who want to give the nearly 12 million illegal immigrants a chance to legitimize their residency either temporarily or permanently, and those who want to tighten security along America's border with Mexico. To that end, the bill would establish several new visas that allow immigrants to work temporarily or put them onto a path to citizenship. But for these visas to be activated, the Homeland Security Department must first certify that several initiatives intended to strengthen America's border have been implemented – the bill's so-called "enforcement triggers." Vitter's amendment would add the US-VISIT program to that list.

"We must have that fully operational before all aspects of this bill are allowed to go into effect. It was authorized 10 years ago, but it is not near to fully operational now. We must make sure that it is a part of this bill's enforcement trigger," Vitter said, adding that there are an estimated 4 million to 5 million people in America who are overstaying their visas. "How can we possibly be ready for the full implementation of this legislation, how can we possibly say we have the enforcement system we need in place without the US-VISIT system, without knowing who exits the country and when, without knowing whether they have overstayed their visa?" Vitter asked.

Ted Kennedy, D-Mass., said adding US-VISIT would be superfluous. "It is our belief those provisions are sufficient, the allocations of resources for the border, the utilization of enhanced border patrols, the enhanced border security, which has been outlined time and again during the course of this debate. They are sufficient. So I would hope at the time that amendment is addressed it would not be accepted," Kennedy said.

By a vote of 48-49, the amendment was rejected. Republicans mostly voted for the amendment, though 12 voted against it. And Democrats mostly voted against the amendment, though 12 voted for it. Thus, the measure went forward without language that would have required the US-VISIT system to be implemented before the measure's visas could be issued.