Why is it necessary to legalize the roughly 11 million currently-illegal immigrants in the U.S. before newly enhanced border security and internal enforcement measures are in place? Sen. Marco Rubio, the leading Republican on the Senate’s Gang of Eight, says part of the reason is that the federal government can’t afford to secure the border on its own and needs financial help from the immigrants themselves, in the form of fines paid when they are legalized.

Rubio made the statement during a radio interview after he voted against an amendment from Republican Sen. Charles Grassley that would have put off legalization until after the border is secure — a position supported by majorities of voters across the political spectrum. Host Andrea Tantaros asked Rubio why he opposed something that was important “to so many in the Republican party?”

Rubio’s first reason was that the U.S. has no other choice than to legalize the 11 million. Enhancing security first would take an estimated four years, and Rubio declared, “We cannot wait another four years with 11 million people living in this country illegally without knowing who they are or why they’re here.”

But there was another reason. “We need to register them as soon as possible, not just to keep the problem from getting worse, but we’re going to require them to pay a fine, and that’s the money that we are going to use to pay for the border security,” Rubio explained. “If we don’t get that fine money from the people that have violated our immigration laws, then the American taxpayer is going to have to pay for border security.”

Of all the expenditures the federal government undertakes, one of the most basic and legitimate is securing the border. It certainly seems like a more reasonable use of taxpayer dollars than, say, creating treadmills for shrimp or sending aid to the Muslim Brotherhood. So why it would be undesirable to have taxpayers pay for security is not clear. Nevertheless, Rubio seemed disinclined to spend public dollars for that purpose. If the fine money is not used, he said, “We’re going to end up borrowing money like we do now for 40 cents out of every dollar, and I want to prevent that from happening.”

Rubio also said he objected to the Grassley amendment because it didn’t include a detailed border security plan, which would leave things up to the Department of Homeland Security. But that was not related to the question of whether or not to legalize the 11 million before new security and enforcement measures are in place. As far as that is concerned, one of Rubio’s main reasons is that we simply can’t afford to do it any other way.