As the Senate is mulling the details of a compromise immigration bill hammered together by the odd couple of Sens. Edward Kennedy and Jon Kyl, and as members of Congress hear from their constituents over the Memorial Day recess, it may be worthwhile to put the issue in historical context. For most of our history, the United States had no restrictions on immigration at all. I am told that my Canadian-born grandfather was a "nickel immigrant": He took the five-cent ferry from Windsor, Ontario, north to Detroit roundabout 1896. This situation resulted from America's strong demand for labor, coupled with its weakness at managing its borders. The government could screen and register immigrants arriving at large ports but couldn't patrol thousands of miles of border.

World War I enlarged and strengthened the federal government, and Congress voted for severe restrictions on immigration in 1921 and 1924. The labor market (and health inspectors) would no longer determine who came here; quotas were imposed on immigration from specific countries to reflect the ethnic composition of the nation in 1890. The apparatus of state was strong enough to enforce these restrictions, and, in any case, there was no market demand for immigrants during the depression of the 1930s and no way for them to come during World War II.

By the time immigration became an issue again, the political impetus for the immigration act of 1965 -- floor-managed by Edward Kennedy -- came from those who expected an influx from Italy, Greece and, if possible, the "captive nations" of Eastern Europe. Few seem to have expected a surge from Latin America or East Asia, although country quotas were applied to immigration from Latin America for the first time.

Why, then, have we had so many Latin immigrants, many of them illegal? Because the apparatus of state has proved weaker than market forces: The old Immigration and Naturalization Service (now U.S. Citizenship and Immigration Services) and the understaffed Border Patrol have been among our least competent federal bureaucracies. And because the family unification provisions of the 1965 act allowed legal immigrants to bring in not just young children but also other relatives ("chain migration"), and because the Fourteenth Amendment makes anyone born in the United States a citizen.

The Kennedy-Kyl bill is built on the assumption that the federal government can effectively channel the flow of immigration. It has country quotas and would admit fewer relatives and more high-skilled workers. It would set a limit on the number of guest workers and a time limit on their stay -- two years in, one year out. It allows for Z visas that would let current illegals remain if they pay certain fines (but not, astonishingly, back taxes), but provides that heads of household must return to their country of origin to be eligible for a green card and get on the path to citizenship.

Amnesty? The thing that is arousing so much fiery opposition to this bill -- embittered cries of "amnesty" -- is that we have tried something like this before and it didn't work. The immigration act of 1986, signed by Ronald Reagan, purported to strengthen the border and to sanction employers of illegal immigrants; in return it gave an amnesty to illegals already here. The amnesty worked, and the Clinton administration scurried to naturalize tens of thousands of immigrants in time for the 1996 election. But border security has not worked. And it turned out to be easy for illegals to buy forged identification papers and unfeasible to prosecute employers who accepted them in apparent good faith.

The advocates of this new bill must convince voters that their plan will work better. They have a decent case to make, such as their call for an identification card with biometric information. Technology has made this more feasible than it was 20 years ago, and the phobia against a national identification card has been weaker since 9/11. Advocates must now convince the critics that such a card would make sanctions against employers enforceable. They must also show that border security will improve: that the 700-mile fence mandated by Congress last fall will actually be built; that unmanned aerial vehicles will reduce illegal crossings; that the larger Border Patrol will be effective; and that the apparatus of state will prove strong enough to prevail against market forces.

Pollster Scott Rasmussen reports that voters aren't dead set against legalizing current illegals. But they must be convinced first that this time, border security is for real.