Such cities will be facing the loss of billions of dollars in federal funds at the least, and possibly worse, because what city officials have been doing constitutes a felony under federal law:
Federal Immigration and Nationality Act
Section 8 USC 1324(a)(1)(A)(iv)(b)(iii)
"Any person who . . . encourages or induces an alien to . . . reside . . . knowing or in reckless disregard of the fact that such . . . residence is . . . in violation of law, shall be punished as provided . . . for each alien in respect to whom such a violation occurs . . . fined under title 18 . . . imprisoned not more than 5 years, or both."
Section 274 felonies under the federal Immigration and Nationality Act, INA 274A(a)(1)(A):
A person (including a group of persons, business, organization, or local government) commits a federal felony when she or he:
* assists an alien s/he should reasonably know is illegally in the U.S. or who lacks employment authorization, by transporting, sheltering, or assisting him or her to obtain employment, or
* encourages that alien to remain in the U.S. by referring him or her to an employer or by acting as employer or agent for an employer in any way, or
* knowingly assists illegal aliens due to personal convictions.
And as Portland mayor Ted Wheeler explained following the unanimous vote by the city council to declare Portland a sanctuary city, it was all about personal convictions: they want the city to be "inclusive" - even if it means violating federal criminal law. So if Sessions chose to do so, he could order federal prosecutors into action. Seeing Mr. Wheeler attempting to explain to a federal judge just why his personal convictions supersede federal law regarding immigration and naturalization would provide a great deal of amusement.
Attorney General Jeff Sessions said Monday he’ll begin punishing sanctuary cities, withholding potentially billions of dollars in federal money — and even clawing back funds that had been doled out in the past.
That would be an amusing development as well, as the city is always complaining about not having enough of our money scrambles to repay funds that they've been deemed not entitled to receive.