The Gang of Eight comprehensive immigration reform changed several times as it raced toward final Senate passage last Thursday. The biggest change, of course, was that it went from being an $8.3 billion bill to a $46.3 billion bill with the Senate’s decision to add the Hoeven-Corker amendment calling for a near-doubling of the Border Patrol.

That change alone rendered the Congressional Budget Office’s estimate of the cost and effectiveness of the bill completely out of date, and the office was unable to make any comprehensive re-assessment of the bill before senators, rushing to vote on the bill before heading home for the July 4 recess, passed the legislation.

Now, the CBO has updated its analysis, and its main finding is that the near-sextupling of the amount of money spent on the Border Patrol would increase apprehensions of immigrants trying to cross the border illegally — but not by much. The original Gang of Eight bill, the one that passed out of the Senate Judiciary Committee, would reduce illegal immigration by about 25 percent, the CBO said. The more expensive amended bill passed by the Senate, according to the CBO, would reduce illegal crossings by as little as 33 percent, and as much as 50 percent. In other words, the Senate’s decision to increase border spending from $8.3 billion to $46.3 billion might yield a pretty small improvement in border security. And even that relatively small gain would take years to achieve, the CBO notes, because it will take a long time to hire the number of Border Patrol agents called for in the Hoeven-Corker amendment.

This is the key passage from the CBO:

CBO estimated that the committee-approved version of S. 744 would reduce the net inflow of unauthorized residents by about one-quarter compared with the projected net inflow under current law. For the Senate-passed version of S. 744, CBO estimates that the net inflow would be reduced by between one-third and one-half compared with the projected net inflow under current law. That effect would not be immediate, as it would take several years before DHS could hire the full number of Border Patrol agents called for in the act.

“CBO today confirmed that this bill falls far short of living up to its sponsors’ promises,” said a Republican Senate Budget Committee spokesman. “Illegal immigration will be reduced by as little as one-third from what it otherwise would be, despite a massive infusion of taxpayer funds at the border.” And with the CBO’s note that it will take years to hire new agents, the spokesman added, “the amnesty will be immediate, with only a distant future promise of enforcement.”