Mayor Bloomberg did us all proud in his testimony before the Senate immigration hearing in Philadelphia. The mayor spoke to the importance of this issue for the city, referring directly to the city’s 500,000 illegal immigrants. Quoth the mayor: “Although they broke the law by illegally crossing our borders or overstaying their visas, and our businesses broke the law by employing them, our City’s economy would be a shell of itself had they not, and it would collapse if they were deported. The same holds true for the nation.”

His testimony was all the more dramatic because it looks like House Republicans are getting what they wanted, though their national hearings are turning out to be a curse instead of a blessing from their own point of view. With President Bush expressing willingness to compromise on the details and senators holding a hearing of their own to highlight the need for actual immigration reform instead of more anti-immigrant rhetoric, House Republicans only looked like obstructionists. If they end up suffering politically for their miscalculation, they’ll have no one to blame but themselves.

The president has now offered them a way out of their corner, suggesting that he would consider a comprehensive bill that rolled out in stages. Under such a compromise, House Republicans would get their enforcement provisions, but as part of a bill that would schedule other elements like expanded visa availability and a path to citizenship to kick in two years from now. Such a compromise could well be the best way forward for immigration reform.

It’s not much of a concession since a guest worker program would take some time to get up and running anyway, while it is possible to take steps to ramp up border enforcement relatively quickly. At the same time, by insisting that border enforcement come only as part of a comprehensive reform package, the compromise entertained by Mr. Bush recognizes that over the long term the only way to stem the tide of illegal immigrants across the Mexican border is to give hardworking people opportunities to come to American legally.

The devil could still be in the details. Some Republicans open to a compromise suggest the guest-worker program should be “triggered” by certain benchmarks in enforcement. If negotiators settle on the wrong triggers, the provision could turn immigration reform into a sham. The right kind of trigger would be something like implementation of an employer verification system to check the status of new employees or installation of new border surveillance technology. The wrong sort would be some target number of illegal immigrants caught by border patrol. Any trigger should be based on establishing the “inputs” for a successful immigration system instead of “outputs” like arrests, an expert on immigration at the Manhattan Institute, Tamar Jacoby, tells us.

By our lights, Mayor Bloomberg has been making the essential point for the Republican camp, if that’s the camp for which he speaks. Any immigration bill will have to recognize that America needs immigrants. The Senate has passed a reform proposal doing just that. The president is willing to consider a compromise that will give House Republicans the enforcement measures they crave while giving the economy the labor it requires. The ball is in the House’s court now.