The signing statement also challenged several other provisions in the bill, including one requiring consultation with Congress about who should be the staff leaders of a newly formed executive branch committee charged with conducting oversight of the government’s response to the pandemic.

Citing his understanding of his power to supervise executive branch staff positions, Mr. Trump said he would not interpret that as mandatory although he anticipated that they would be consulted anyway.

Mr. Trump’s legal team is led by Attorney General William P. Barr, who is known for his embrace of a maximalist interpretation of presidential power, including the so-called unitary executive theory. Under that doctrine, laws that bestow independent decision-making authority on subordinate executive branch officials are unconstitutional because the president wields total control over deciding how to exercise executive power over the government.

Presidential signing statements are official documents issued by presidents when they sign new legislation into law. They leave a record of the president’s understanding of the meaning of newly created statutes and essentially instruct the rest of the executive branch to interpret the laws in the same way. Congress has no opportunity to veto them.

The device becomes subject to dispute when presidents use it to mount a constitutional challenge to a new law that imposes some requirement or limitation on their power, essentially nullifying the new limit in the eyes of the executive branch. Often such disputes center on matters for which there is scant likelihood that the matter will come before a court for judicial judgment, giving the executive branch final say as a practical matter.

Signing statements, which are not mentioned in the Constitution, were once rare, but presidents started to issue them more frequently starting in the second term of the Reagan administration.

They became controversial under President George W. Bush, who used them to challenge more provisions of new laws than all previous presidents combined, including asserting a right to authorize officials to bypass laws like a torture ban and oversight provisions of the USA Patriot Act he had agreed to as a condition of breaking a Senate filibuster to get an extension of the law passed when it was about to expire.