Mayor Michael Bloomberg didn’t make many friends when he offered his own idea for saving Detroit, which has lost one-fourth of its population over the last decade.

Speaking on “Meet the Press” on NBC earlier this month, he suggested that Congress “pass a law letting immigrants come in as long as they agree to go to Detroit and live there for five or 10 years, start businesses, take jobs, whatever.  You would populate Detroit overnight because half the world wants to come here.”

Detroiters like Mayor Dave Bing were displeased (the fact that Mr. Bloomberg had called him a “great mayor” didn’t quell his pique). “I don’t know what he was on,” Mr. Bing said, pointing out that his city had scarcely enough jobs to sustain the people already there. Yet Mr. Bloomberg had the big picture exactly right: immigrants and economic vitality go together. That was certainly the experience of New York City, which was on life support in the 1970s until a transfusion of immigrant energy and entrepreneurship brought it roaring back.

Renewal by immigrants is the fundamental American narrative, the story of people in ships, then covered wagons, coming to settle and make fruitful a land that rewarded their courage and grit. Except now that story is scorned and discarded, along with many of those immigrants.

Bills to streamline and increase legal immigration die in Congress. There are no visas of the type Mr. Bloomberg imagines, though we could use immigrant entrepreneurs in Detroit, Buffalo, New York City — all over. Nearly 150 years after President Lincoln signed the Homestead Act, the new frontier is in the inner city, not way out West. There is no federal or state Department of Urban Homesteading, but — DUH — maybe there should be.