Mayor Bloomberg has opened up a terrific theme in challenging Governor Romney and the other candidates running for the presidency in 2008 by, amongother things, seeking to slash funding for cities that don’t strictly enforce immigration laws. The mayor did not criticize Mr. Romney, or anybody else, by name, our Jill Gardiner reported yesterday at www.nysun.com, but he declared, “Boy, let them come,” and held up the example of the city he has led to one of its finest hours. “I can’t think of any laboratory that shows better why you need a stream of immigrants than New York City.”

Our hope is that this signals a decision by the mayor to lift his sights, as he regards the possibility of a presidential run, and to “aim high,” as we put it in an editorial on July 18 that encouraged him to tap into the big themes at play in the current political fray. “Immigration,” we wrote, “is a presidential topic, one on which the mayor is an advocate of a clear, realistic, pragmatic, open, and growth-oriented approach.” We noted that there are huge blocks of voters up for grabs on the issue, which is one where a middle ground is opening up between the rightists and the leftists.

One of the things we noted is that this is an issue on which there is differentiation between the mayor and the others, an issue “where he has automatic authority as the mayor of a city that is the gateway for millions of immigrants, legal and otherwise.” In his remarks yesterday, Ms. Gardiner reported, the mayor pointed to the city’s low crime rate, its improving schools, and its thriving economy. “If that isn’t example enough as to why you need immigrants coming in, I don’t know what to tell anybody,” Mr. Bloomberg said.

The mayor spoke in the context of a movement to cut funding for so-called sanctuary cities, that is, cities that declare themselves “sanctuaries” and fail to enforce immigration laws as a matter of policy. New York isn’t an official sanctuary city, but it is the premier example in the country, perhaps the world, of what economic horsepower can be generated by an influx of aspirants eager to participate in the American dream. With President Bush’s immigration reform stalled in the Congress, here is a theme Mr. Bloomberg can press to his advantage as he maneuvers toward 2008, and judging by the feckless approach of both the Democrats and the formerly pro-growth Republicans, he could well have the issue to himself.