President Obama chairs a meeting of the National Security Council next to Defense Secretary Ashton B. Carter and gets an update on the fight against the Islamic State on Thursday at the Pentagon. (Dennis Brack/European Pressphoto Agency)

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 GOP 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 further questions on the subject would receive “variations on the same theme.”

President Obama responded to a question about Republican presidential nominee Donald Trump and the classified intelligence briefings he receives, at a press conference on Aug. 4 at the Pentagon. (Reuters)

The president’s remarks followed an extraordinary denunciation of Trump’s candidacy earlier 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 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 ISIL, is “inevitably going to be defeated,” but he predicted that the dispersed terrorist networks it spawns are likely to continue 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 last year, as proof that the group is “not invincible,” and said that U.S.-backed Iraq 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.

President Obama praised Muslim Americans serving in the military amid a controversy about Donald Trump’s comments on the parents of a fallen Muslim soldier at a press conference at the Pentagon on Aug. 4. (Reuters)

“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. Even ISIL’s leaders know they’re going to keep losing.”

Earlier this week, the Pentagon disclosed that the United States conducted airstrikes on an Islamic State stronghold in Sirte in a significant expansion of the U.S. campaign against the Islamic State.

The strikes came at the request of Libya’s Western-backed unity government as its forces battled to reclaim the Mediterranean coastal city, which became an important Islamic State stronghold after militants seized it last year.

[U.S. strikes Islamic State stronghold in Libya]

In his opening remarks Thursday at the Pentagon, Obama said the Islamic State’s losses in Iraq and Syria are prompting it to shift to “high-profile terrorist attacks” aimed at the United States and various other countries.

And he acknowledged that crushing the Islamic State on the battlefield “will not be enough, so long as their twisted ideology persists.” He said the group has figured out that if it can get a small cell or even one person to carry out an attack that kills scores of people, that “still creates the kinds of fear and concern that elevates their profile.”

The greatest danger posed by the group was one of overreaction, Obama said.

“How we react to this is as important as the efforts we take to destroy ISIL,” Obama said. “The reason it is called terrorism is that these are weak enemies that can’t match us in conventional power, but what they can do is make us scared.”

Obama warned against proposals from Trump and other Republicans to carpet-bomb Islamic State-held territory or institute religious tests that would bar Muslims from entering the United States.

“In order for us to ultimately win this fight, we cannot frame this as a clash of civilizations between the West and Islam,” he said, arguing that such a strategy would play into the radical group’s hands and undermine the fabric of American society. “That plays exactly into the hands of ISIL and the perversions and perverse interpretations of Islam that they’re putting forward. It makes us weaker and makes us more vulnerable,” Obama said.

Many of the questions that came the president’s way focused on Trump.

Pressed on whether he had qualms about Trump receiving classified intelligence briefings, Obama said he would follow the law but warned that those who aspire to the White House “have got to start acting like president. And that means being able to receive these briefings and not spread them around.”

Asked to respond to Trump’s assertion that the election was being rigged, Obama replied: “I don’t even know where to start on answering this question,” he said. “Of course the elections will not be rigged. What does that even mean?”

On the question of whether Trump was qualified to handle nuclear weapons, Obama said that Americans are counting on their next president to be somebody who has the right “temperament and good judgment.”