Amid a generally upbeat assessment of the campaign against the Islamic State — known internally now as “D-ISIS” for “Defeat ISIS,” using another name for the group — Mr. Mattis struck a sobering note, saying the fight “is not going to be over soon.”
Mr. Mattis was joined by Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, and Brett McGurk, the United States special envoy to the coalition against the Islamic State.
The timing of their comments, which represent the most comprehensive report on the Trump administration’s campaign against the Islamic State, was not happenstance: It came as Mr. Trump headed out on a nine-day visit to Saudi Arabia and Europe, where he will not only seek to rally support for the campaign against the Islamic State in Syria and Iraq, but also try to gain commitments from NATO for more troops in Afghanistan.
Mr. Trump seemed pleased enough with his top generals on Friday to renominate General Dunford and Gen. Paul J. Selva of the Air Force, the vice chairman of the Joint Chiefs of Staff, each to a second two-year term.
At the Pentagon, General Dunford ticked off some of the campaign’s accomplishments, including reclaiming 55 percent of the territory the Islamic State has seized in Syria and Iraq since 2014. He said the effort has also significantly reduced the group’s ability to finance its terrorist operations and draw new recruits into Iraq and Syria, down to fewer than 100 a month from a peak of 1,500 a month.
Other senior American officials, including Nicholas J. Rasmussen, the director of the National Counterterrorism Center, have offered a more measured analysis of the impact of the global fight. Mr. Rasmussen said this month that “the global reach of ISIS remains largely intact” despite the group’s territorial losses.