WASHINGTON — As he prepared to head off for his summer vacation, President Obama on Thursday made clear that he could use a break from talking about Donald Trump.

Obama was asked during a news conference at the Pentagon about the Republican nominee’s fitness to receive national security briefings, his charges that the presidential election might be rigged and his ability to handle the country’s nuclear arsenal.

After the third question on Trump, which focused on the nuclear issue, the president offered a blanket response that would cover any further inquiries about the Republican nominee and his fitness for the Oval Office.

“I would ask all of you to just make your own judgment,” Obama said. “I’ve made this point already multiple times. Just listen to what Mr. Trump has to say and make your own judgment with respect to how confident you feel about his ability to manage things like our nuclear triad.” To ward off further inquiries, the president warned that any more questions on the subject would receive “variations on the same theme.”

The president’s remarks followed an extraordinary denunciation of Trump’s candidacy this week in which Obama described him as “unfit to serve” and called on Republicans to withdraw their endorsements. “What does this say about your party that this is your standard-bearer?” he challenged.

Obama is scheduled to leave Saturday for a vacation with his family on Martha’s Vineyard in Massachusetts through Aug. 21.

Before he departed, Obama was at the Pentagon, where he received a two-hour briefing from his top national security advisers on the expanding war against the Islamic State in Iraq, Syria and most recently Libya, where U.S. planes have been bombing in support of a government offensive near Sirte.

Obama vowed that the Islamic State, also known as ISIS and ISIL, is “inevitably going to be defeated,” but he predicted that the dispersed terrorist networks it spawns are likely to keep trying to launch attacks after the group loses its major strongholds in Iraq and Syria.

“As we’ve seen, it is still very difficult to detect and prevent lone actors or small cells of terrorists who are determined to kill the innocent and are willing to die,” Obama said. “And that’s why … we’re going to keep going after ISIL aggressively across every front of this campaign.”

Obama pointed to a string of battlefield defeats suffered by the Islamic State in the past year as proof that the group is “not invincible,” and said that U.S.-backed Iraqi forces would use a recently recaptured air base as a hub to take back Mosul, the Islamic State’s largest stronghold in Iraq.

Obama said he was confident that the Islamic State would continue to lose territory as Iraqi and Syrian forces, backed by American air power, close in on Mosul, Raqqa and strongholds near the Turkish border.

“ISIL has not been able to reclaim any significant territory that they have lost,” Obama said. “I want to repeat, ISIL has not had a major successful offensive operation in either Syria or Iraq in a full year.”