A new estimate from the Congressional Budget Office suggests that the final version of the Senate immigration bill would cut future illegal immigration flows by 33 to 50 percent.

The old CBO estimate, remember, suggested that the original Gang-of-Eight immigration bill would cut future flows by 25 percent and grant amnesty to 7.7 million unauthorized immigrants who are living in the country.

Our back-of-the-envelope estimates suggested that that would leave about 5 million or so illegal immigrants living in the United States.

But then the Senate modified its bill, passing the Corker-Hoeven amendment that would spend $30 billion to double the number of federal border agents, complete 700 miles of fencing and expand radar and aerial drone surveillance along the border.

As a result, CBO says, the net inflow of future illegal immigration "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."

The final bill would also have a smaller effect on the deficit, thanks to all the additional outlays for border security. CBO estimates that the bill would lead to a net savings of $135 billion over the next decade, compared with $200 billion for the original bill.

Further reading:

--Here's how the U.S. population would change under immigration reform.

--Border security is the key to immigration reform. So how do we measure it?