As Rick Moran noted, President Trump's threat to cut off funding for sanctuary cities  is about a slice of funding of a very small $27-million pie, because only one federal grant program would be subject to this rule.  In practice, a major city might lose a five- or six-figure grant.  But that's pocket change for big cities with budgets in the hundreds of millions or even billions of dollars.  I was surprised to learn that Trump's threat to "cut off" funding doesn't even apply to all Justice Department grants, just the ones in this one tiny program.

Now imagine if Trump were serious about punishing sanctuary cities.  Imagine if he cut off all discretionary grants to cities that do not cooperate with ICE.  How much money are we talking about?  Let's take New York City as an example.  In 2015, it was seven billion dollars.

Over the past five years, total federal aid to New York City has declined from $7.9 billion in 2011 to just under $7.0 billion in 2015, a decrease of roughly $933 million, or nearly 12 percent. 

• Federal aid, excluding stimulus and recovery funding, totaled $32.3 billion, or just over 85 percent of total federal aid received over the years 2011 through 2015.
• Three city agencies received a combined $22.5 billion, or roughly 70 percent, of federal aid during the five-year period: the Department of Education ($8.4 billion), Human Resources Administration ($7.7 billion), and Administration for Children’s Services ($6.4 billion).
• Three other departments, Housing Preservation and Development, Homeless Services, and Health and Mental Hygiene, also received a significant share of federal aid ($2.4 billion, $1.6 billion, and $1.6 billion, respectively) during the period.

Just five federal grant programs, excluding stimulus and disaster recovery funds, accounted for $16.8 billion, or over half, of the city’s aid from Washington.

Now, can you imagine what would happen if President Trump got serious about sanctuary cities and cut off all grants to New York City?  NYC would be faced with a severe financial crisis.  It would be forced to obey federal law.

The city would sue, of course, but a lawsuit could take years to resolve.  Judges are very good at ordering the government not to do things, but how can a judge order the federal government to issue grants to a city at a certain rate, since they are, by definition, discretionary?  Trump could tie up the proceedings for years by arguing that sanctuary jurisdictions are not meeting requirements for various grant programs.

Instead, Trump "threatens" uncooperative jurisdictions with the loss of $100,000.  Or $20,000.  Or $5,000.  What, then, is the purpose?