Democratic mayors are rushing to protect their cities’ businesses from President Donald Trump’s promise to cut federal funding from “sanctuary” cities which refuse to help enforce the nation’s popular immigration laws.

“Half the new businesses in Chicago and the state of Illinois come from immigrants, nearly half,” Chicago Mayor Rahm Emanuel told reporters on Monday. , while conflating the economic impact of legal and of illegal immigration. “We want to continue to welcome people, welcome their ideas, welcome their families to the city of Chicago, who want to build the American dream for their children and their grandchildren,” he said in New York. Trump’s opposition to sanctuary cities would not have an impact on legal immigration.

“We will fight to protect the safety and dignity of all Angelenos, and we will work closely with our representatives in Congress to make sure that Los Angeles does not go without federal resources that help protect millions of people every day,” said L.A.’s Mayor Eric Garcetti, whose “sanctuary city” policies hinder enforcement of immigration rules.

“We are going to become this administration’s worst nightmare,” Melissa Mark-Viverito, the Speaker of the New York City Council, claimed Monday. She spoke at a meeting of pro-immigration mayors from many cities Seattle, Chicago, Denver, New York and Philadelphia.

Legal and illegal immigrants play a huge role in expanding the economies — and the national political clout — of major cities. In contrast, most American cities rely on young Americans, new companies, new technology, and greater productivity to grow their economies.

The Los Angeles metro area, for example, hosts roughly 4.5 million legal and illegal immigrants who boosted the city’s size by 50 percent, according to data provided by the business-backed Partnership for a New American Economy. Collectively, the immigrants spent $93 billion on goods and services in 2014, boosting the size of  L.A.’s economy — even as per-person income has stalled or shrunk in the region since before 2000.

Illinois’ population is boosted by 14 percent because of legal and illegal immigration, while consumer spending was increased by $40 billion in 2014, according to PNAE, which also declined to explain the impact of the new migrants on the city’s population, which is now suffering from a massive wave of murders. “Chicago was built on the back of immigrants and our future is hitched to the wagon of immigrants who come to the city,” Mayor Emanuel said Monday. “I would say that the [administration’s] approach of penalizing cities, cities that are driving the economy, driving the energy of the United States – and they do it because we bring people of all different backgrounds to work together – that’s just the wrong approach.

New York state and city has 4.5 million legal and illegal immigrants, which boosted the state’s population by 25 percent and overall spending by $103 billion, according to 2014 data provided by PNAE, which pushed for passage of the 2013 “Gang of Eight” immigration-and-amnesty bill. The PNAE data did not say if the immigrant population has increased the per-person income of native-born Americans.

The population of the Denver metro area has expanded 15 percent because of immigration, and local spending was boosted by roughly 2.1 billion in 2014, says PNAE.

The PNAE also says illegal immigration helps grow the nation’s economy, although it does not highlight the costs imposed on American workers and taxpayers:

Yet, while the undocumented population frequently comes under fierce criticism, the data shows that a large number of the 11.4 million undocumented immigrants here are working, paying taxes, and even starting their own businesses. They also play an integral role in our economy, often filling jobs in agriculture, construction, and hospitality that would otherwise remain vacant.

The PNAE group is run by major business executives who gain from the importation of new workers and new consumers.

Economies grow if when they add more people, because those people need to eat, live in homes, purchase consumer goods. That doesn’t mean that the native-born population benefits from that growth.

But studies by Harvard Professor George Borjas, and corroborated by the National Academies of Sciences, show that new low-wage migrants help reduce Americans’ wages by roughly $500 billion per year, nearly all of which is transferred to investors and company owners. The business groups also gain up to $60 billion per year when state and local taxpayers are required to fund welfare and support of poor immigrants.

Garcetti and other Democrats hope to block Trump’s immigration enforcement measures via lawsuits.

“We are absolutely prepared in the courts — together with the other cities and states — to reaffirm what the Supreme Court literally just decided last year on the Tenth Amendment,” Garcetti told reporters.  “You can take away funding for a specific program if you don’t adhere to specific requirements of that program, but we don’t have funding that is for the cooperation of our immigration federal officials and our local officials,” he argued.

The Democrats were defying a Monday request by Attorney General Jeff Sessions to help enforce the nation’s immigration laws. “I urge the nation’s states and cities to carefully consider the harm they are doing to their citizens by refusing to enforce our immigration laws,” Sessions told reporters gathered at the White House on Monday, adding that cities which oppose federal law would lose federal funding, including federal grants.

In his Monday appeal, Sessions told reporters that:

The Department of Justice has a view to enforce our nation’s laws, including our immigration laws.  Those laws require us to promptly remove aliens when they are convicted or detained of certain crimes.  The vast majority of American people support this commonsense requirement.  According to one recent poll, 80 percent of Americans believe that cities that arrest illegal immigrants for crimes should be required to turn them over to immigration authorities.  Unfortunately, some states and cities have adopted policies designed to frustrate this enforcement of immigration laws.  This includes refusing to detain known felons on the federal detainer request, or otherwise failing to comply with these laws.

… DUIs, assaults, burglaries, drug crimes, gang rapes, crimes against children, and murderers — countless Americans would be alive today and countless loved ones would not be grieving today if these policies of sanctuary cities were ended.  Not only do these policies endanger lives of every American — just last May, the Department of Justice inspector general found that these policies also violate federal law…

Today, I’m urging states and local jurisdictions to comply with these federal laws, including 8 U.S.C. Section 1373.  Moreover, the Department of Justice will require that jurisdictions seeking or applying for Department of Justice grants to certify compliance with 1373 as a condition of receiving those awards.

This policy is entirely consistent with the Department of Justice’s Office of Justice Program’s guidance that was issued just last summer under the previous administration.  This guidance requires state and local jurisdictions to comply and certify compliance with Section 1373 in order to be eligible for OJP grants…

The Department of Justice will also take all lawful steps to claw back any funds awarded to a jurisdiction that willfully violates 1373.  In the current fiscal year, the Department of Justice’s Office of Justice Program and Community Oriented Policing services anticipates awarding more than $4.1 billion in grants…

The American people want and deserve a lawful system of immigration that keeps us safe, and one that serves the national interest.  This expectation is reasonable, just, and our government has the duty to meet it, and we will meet it.

Each year, the federal government provide residency to roughly 1 million new legal immigrants and provide work permits to roughly 1 million new foreign contract workers, just as 4 million young Americans enter the workforce. The nation’s official population of 321.4 million also includes 11 million illegal immigrants, of which roughly 8 million are employed.