The bipartisan Gang of Eight has released its new comprehensive immigration proposal. Before the bill was made public, supporters said it would require the government to maintain 100 percent surveillance of the U.S. border with Mexico and catch 90 percent of those who try to cross it illegally. They spoke very clearly: 100 percent surveillance and 90 percent apprehension.

Now the bill is out, and the wording is not quite as clear. The bottom line is that it does not mandate 100 percent surveillance and leaves questions about what 90 percent apprehension actually means.

The bill requires the secretary of Homeland Security — at the moment Janet Napolitano, who maintains that the U.S. border with Mexico is already secure — to “submit a strategy, to be known as the ‘Comprehensive Southern Border Security Strategy,’ for achieving and maintaining effective control between the ports of entry in all high risk border sectors along the Southern border…”

The bill defines “effective control” as “the ability to achieve and maintain, in a Border Patrol sector, (A) persistent surveillance; and (B) an effectiveness rate of 90 percent or higher.”  And the bill defines “effectiveness rate” in a sector as “the percentage calculated by dividing the number of apprehensions and turn backs in the sector during a fiscal year by the total number of illegal entries in the sector during such fiscal year.”

A few phrases jump out: “high risk,” “effectiveness rate,” and “persistent surveillance.”

The bill defines “high risk” as “a border sector in which more than 30,000 individuals were apprehended in the most recent fiscal year.”  Using Border Patrol numbers from 2012, it would appear that the standard would apply to three of the nine sectors of the U.S. border with Mexico: the Tucson sector in Arizona and the Rio Grande Valley and Laredo sectors in Texas. The other six, with 2012 apprehensions ranging from 3,964 to 28,461, would not be affected.

It appears that the three sectors are the only ones that would have to be under “persistent surveillance.” But what does “persistent surveillance” mean? The bill doesn’t say.  And whatever it is, it would apply only to “high risk” border sectors.

The most serious ambiguity might be in the concept of “effectiveness rate.” How will Napolitano, or her successor at the Department of Homeland Security, determine when the effectiveness rate reaches 90 percent?  The calculation has to start somewhere, and it is with the total number of people attempting to cross the border illegally.  Napolitano has to certify that the Department of Homeland Security is catching nine out of ten of them — a calculation that starts with that total number of illegal crossing attempts.

That’s where the confusion will come in. New ways of surveying the border have shown that the Department has greatly underestimated the number of people attempting to cross any given part of the border. Experimental programs with the new drone-based Vader surveillance system have shown that at least twice as many illegal immigrants crossed the border in some areas as were apprehended. That means the government, which thought it had a pretty high apprehension rate, was actually catching less than 50 percent of illegal crossers.

So now, if the new 90 percent standard becomes law, how would the effectiveness rate be calculated? Would it be 90 percent of the old, pre-Vader estimates of illegal immigrants crossing the border? If so, that would likely mean that in fact the U.S. would be apprehending far less than 90 percent of those actually crossing the border. Or would it be 90 percent of up-to-date Vader-generated numbers, which would suggest that U.S. officials are much closer to capturing nearly all the illegal crossers?

The bill requires that Napolitano, or her successor, specify in the Comprehensive Southern Border Security Strategy the “surveillance and detection capabilities developed or used by the Department of Defense to increase situational awareness” and also that she specify “the fixed, mobile, and agent portable surveillance systems and unarmed, unmanned aerial systems and unarmed, fixed-wing aircraft and necessary and qualified staff and equipment to fully utilize such systems.” It is not clear how much say Congress will have in requiring that Napolitano actually use the new technology, and where she should use it.

More later.