“The policies aren’t changing; in some ways, they’re getting worse,” said Stephen Wertheim, a historian and the co-founder of the Quincy Institute for Responsible Statecraft, a new research group in Washington financed by prominent billionaires — George Soros, a liberal, and Charles Koch, a conservative — who advocate American military restraint.

In some corners, though, there has been pushback against the notion that a lower troop presence leads to greater security. Proponents of the forever war point to President Barack Obama’s withdrawal from Iraq in 2011 as paving the way for the rise of the Islamic State in 2014.

But that ignores a whole set of circumstances, including the formal withdrawal agreement Mr. Bush had previously reached with the Iraqi government because the Iraqis wanted the Americans out, and the role of the Syrian civil war in creating the Islamic State. Most important, it ignores the lack of political will among American citizens for continuing the war.

Some lawmakers are trying to revoke the war authorizations of 2001 and 2002 — the first used for fighting Sept. 11-related terrorism and the second for invading Iraq — and looking for other ways to constrain Mr. Trump’s ability to expand the wars. In January, senators in the Republican-led chamber sponsoring legislation to limit military action against Iran said they had enough votes to pass the bill, the War Powers Resolution. The Democratic-led House passed a similar measure last month.