On January 25 President Donald Trump signed an executive order denying federal funds to sanctuary cities, which are those jurisdictions that either won't help the federal government round up and deport undocumented immigrants or otherwise refuse to participate in the enforcement of federal immigration laws. This executive order debases the U.S. Constitution in three significant ways. Let's take them in turn.

The 10th Amendment

In 2007 the U.S. Supreme Court decided the case of Printz v. United States. At issue was whether the federal government could lawfully order state officials to enforce certain provisions of the 1993 Brady Handgun Prevention Act. The feds lost the case—and rightfully so. The federal government's actions violated the 10th Amendment.

"The Federal Government may neither issue directives requiring the States to address particular problems," declared the majority opinion of Justice Antonin Scalia, "nor command the States' officers, or those of their political subdivisions, to administer or enforce a federal regulatory program." In other words, the federal government may not commandeer the states for federal purposes. Scalia's opinion in Printz plainly forbids the Trump administration from ordering sanctuary cities to enforce federal immigration laws.

The Spending Clause

Article I, Section 8 of the Constitution grants Congress the power to tax and spend. But this power is not unlimited. For example, it is unconstitutional to impose what the Supreme Court has called "coercive" conditions on federal spending grants to the states. This principle was recently affirmed by seven Supreme Court justices in the 2012 Obamacare case National Federation of Independent Business v. Sebelius. At issue was whether Congress exceeded its Spending Clause powers when it threatened to cut off all existing Medicaid funding to any state that refused to expand Medicaid in accordance with the new health care law.

The federal government's Medicaid expansion amounted to a "gun to the head," the Supreme Court held. "A State that opts out of the Affordable Care Act's expansion in health care coverage…stands to lose not merely 'a relatively small percentage' of its existing Medicaid funding, but all of it." That sort of "economic dragooning…leaves the States with no real option but to acquiesce."

Trump's attempt to dragoon sanctuary cities by threatening to cut off their federal funding is unconstitutional for the exact same reasons.

The Separation of Powers

The U.S. Constitution sets forth a system of limited and enumerated federal powers. The federal spending power (including the power to attach non-coercive conditions on federal spending) is located in Article I, Section 8. Open your copy of the Constitution and turn to Article I. You will find that it pertains exclusively to Congress. The limited and enumerated powers of the president are spelled out in Article II.

What this means is that Trump's executive order on sanctuary cities seeks to usurp a core congressional function. That makes it an unconstitutional violation of the separation of powers. Whether Trump likes it or not, no president has the unilateral authority to act in this manner.

In sum, Trump's attack on sanctuary cities is a malignant executive power grab that subverts the Spending Clause and tramples the 10th Amendment. It is an affront to both the text and structure of the Constitution.