The Paris Agreement is essentially a collection of voluntary emissions-slashing pledges from about 200 nations. Countries are not legally bound to meet their targets, but they are supposed to report their progress to the United Nations.

The United States under the Obama administration pledged to cut emissions about 28 percent below 2005 levels by 2025. Mr. Trump has previously said his administration will no longer work toward that target, and the State Department has failed for more than two years to submit documents showing what the United States is doing to reduce emissions.

The Trump administration also has taken actions to limit states’ abilities to cut their own emissions, recently revoking a waiver that California had under the Clean Air Act to set automobile tailpipe pollution standards at stricter levels than the federal government. On Wednesday the Justice Department sued California to block part of a regional greenhouse gas emission program that included Quebec, arguing the agreement violates the constitutional prohibition on states making their own treaties with foreign governments.

At various points since Mr. Trump vowed to leave the Paris Agreement, which he has called “job-killing” and “a bad deal,” he has hinted at the possibility of staying in if he could renegotiate better terms.

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But the administration never made serious efforts to discuss with other countries what precise terms of the voluntary pact it would want to revisit. The handful of administration officials who had pressed Mr. Trump to remain in the agreement, such as Gary D. Cohn, the former director of the National Economic Council, and Rex W. Tillerson, the former secretary of state, have left and been replaced by fierce opponents of the accord.

According to three current and former administration officials , who asked not to be named because they were not authorized to discuss administration briefings, the White House has not wavered in its plans to send the formal notice of withdrawal to the United Nations and is only internally discussing whether to do it at the earliest possible moment or wait.

Malik Russell, a spokesman for The Climate Mobilization, a youth-led environmental advocacy group, called the decision “insanity” and at odds with popular opinion.