President Trump appears to be declaring independence from outside constraints on how he nominates judges, signaling that he is looking for loyalists who will uphold his agenda and denouncing the conservative legal network that helped him remake the federal judiciary in his first term.

Late Thursday, after a ruling struck down his tariffs on most imported goods, Mr. Trump attacked the Federalist Society, leaders of which heavily influenced his selection of judges during his first presidency.

“I am so disappointed in The Federalist Society because of the bad advice they gave me on numerous Judicial Nominations,” Mr. Trump asserted on social media. “This is something that cannot be forgotten!”

Hours earlier Thursday, the Justice Department severely undercut the traditional role of the American Bar Association in vetting judicial nominees. A day before, Mr. Trump picked a loyalist who has no deep ties to the conservative legal movement for a life-tenured appeals court seat, explaining that his pick could be counted on to rule in ways aligned with his agenda.

Together, the moves suggest that Mr. Trump may be pivoting toward greater personal involvement and a more idiosyncratic process for selecting future nominees. Such a shift would fit with his second-term pattern of steamrolling the guardrails that sometimes constrained how he exercised power during his first presidency.

But it could also give pause to judges who may be weighing taking senior status, giving Mr. Trump an opportunity to fill their seats. Conservatives have been eyeing in particular the seats of the Supreme Court justices Clarence Thomas, who will turn 77 next month, and Samuel A. Alito, 75.