The US federal courts have generally avoided ruling on this issue.  However, Hale v. Henkle, 1905, is one of the most quoted US Supreme Court cases in American legal history.  While it does not address common law trusts per se, it affirms the individual’s right to enter into private contract without interference from the government, as long as that individual is not harming anyone or violating the rights of anyone in so doing.
One interesting article along these lines can be found at https://law.marquette.edu/facultyblog/2010/10/the-u-s-supreme-courts-most-important-decision-affecting-the-law-of-trusts-estates-was-decided-a-very-long-time-ago.  It says, in part:
By: J. Gordon Hylton, October 31, 2010, Legal History, U.S. Supreme Court
“. . . The United States Supreme Court rarely addresses issues directly involving the law of wills and trusts.  Like most legal questions involving the transfer of private property between private citizens, such matters have usually been left to state courts.  Federal courts have even adopted special rules, like the so-called “probate exception to federal jurisdiction,” to keep wills- and trusts-related matters out of federal courts.  (This principle, described by Judge Richard Posner as “one of the most mysterious and esoteric branches of the law” prohibits federal courts from entertaining a suit that encroaches on the jurisdiction of state probate courts.) . . .
“. . . To find a Supreme Court decision that significantly altered the course of the development of the law of trusts and estates, one arguably has to go back to 1875 and the case of Nichols v. Eaton, 91 U.S. 716 (1875).  That case recognized the legitimacy of the spendthrift trust and paved the way for its widespread acceptance as a legal means of protecting one’s beneficiaries from the meritorious claims of their creditors . . .”
Also, here is a salient gem on the IRS website which clearly acknowledges the official recognition of the legitimacy of common law trusts:
... " Unlike corporations, LLCs, or limited partnerships, trusts generally do not file their governing instrument with the State to become legal."
- - from “Exempt Organizations -Technical Instruction Program for FY 2003 - Trusts: Common Law and IRC 501(c)(3) and 4947”, by Ward L. Thomas and Leonard J. Henzke, Jr.  (https://www.irs.gov/pub/irs-tege/eotopica03.pdf)