The traffic roars
And the sirens scream
You look at the faces
It's just like a dream
Over the past couple of years, the term 'sanctuary cities' has been applied to cities whose political officials have refused to enforce federal immigration laws. Why have they done so? Sanctuary cities are almost exclusively under the control of Democrats. Because Democrats generally view voter blocks sympathetic to immigrant causes as valuable sources of political capital, their creation of sanctuaries for illegal immigrants can be seen as a thinly veiled strategy for winning votes.
Are sanctuary cities legal? As Judge Nap argues, yes. Local authorities are not obligated to help the feds with manpower or other resources to enforce federal law in local jurisdictions. The Supreme Court has ruled in previous cases that the federal government cannot force local officials to enforce federal law; the feds must enforce it themselves.
The Court's rationale is that such compulsion would violate the Guarantee Clause of the Constitution which guarantees a representative form of government in every state. If the feds interfered with the will of elected state officials on how to spend state resources (read: tax dollars), then representative government would be constitutionally impaired in those states.
To get around this legal inconvenience, the federal government has frequently provided funding to states that is contingent on state cooperation in particular matters. During the Reagan administration, for instance, the feds dangled dollars in front of states for interstate highway repairs under the condition that states reduce speed limits to 55 miles/hr. If states didn't want to lower their speed limits, then they were free to reject the funds. Subsequent ruling by the Supreme Court validated the legitimacy of what resembles a contract.
In other cases, however, the federal government has threatened to pull funding from states who refuse to comply with a federal demand that was not specified when the monies were first sent to the states. For example, in a move designed to force states to expand Medicaid under Obamacare, the federal government threatened to cut Medicaid funding to states who didn't do so. In one of the few Supreme Court rulings related to Obamacare that made sense, this initiative was ruled invalid by the Court.
Not only does such a practice by the federal government violate the principle of federalism, but it is not good contracting practice.
A similar situation has arisen in the context of the sanctuary cities. Under the Obama administration, funds were offered to sanctuary cities with no strings attached related to federal immigration law enforcement. Now, the Department of Justice under the Trump administration wants to impose such strings retroactively. As Judge Nap notes, that won't fly in the courts and any legal challenge on withholding Obama era funding should favor the sanctuary cities.
What the Trump administration can do is work with Congress on future funding packages that do require state cooperation in immigration law enforcement if states want those funds.
In the case of sanctuary cities we are witnessing principles of federalism and nullification in action--both of which are healthy and favorable for liberty. Democrats and Republicans, of course, tend to like these principles when they work in their political favor and detest them when they don't.