A fine idea in theory

Even if the border could miraculously be made airtight against trespassers, it would do nothing to stop foreigners from coming on tourist or student visas and then staying on after they are supposed to leave. According to the Pew Hispanic Center, as many as 45 percent of the foreigners here illegally arrived with the blessing of the law. Build a 2,000-mile fence, and more will come that way.

Hardliners think the way to get rid of illegal immigrants is to get rid of the jobs they fill. In the Senate bill endorsed by President Bush, advocates of tougher enforcement got a new system for employers to verify that their workers are entitled to be here. Anyone newly hired (and, in time, anyone with a job) would have to pass a check of federal databases.

It's a fine idea in theory, but note that it requires government authorization for every employment decision in a large, dynamic economy, an approach that is just slightly at odds with the free market. It also presumes a level of efficiency that conservatives do not usually expect of government.