"Success looks like an ISIL that no longer threatens our friends, can't accumulate followers and threaten Muslims in Syria, Iraq, or otherwise," McDonough told NBC "Meet the Press" host Chuck Todd. "And that's exactly what success looks like."
To achieve that, the United States will wage a counter-terrorism fight like those in Yemen and Somalia, "where we will take the fight to our enemies without putting our ground troops into the effort," McDonough said, echoing President Barack Obama's prime-time speech last week.
He admitted, like many military experts, that ground troops are needed, but pointed out to Todd that Obama's plan calls for training opposition troops in Iraq and Syria to handle the ground battles.
"That's why we want to make sure that this coalition brings Sunnis to the fight," said McDonough, who appeared not only on the NBC program, but also on ABC, FOX, and CNN's Sunday news shows to discuss the ongoing ISIS situation.
There has been some disagreement on whether to term the fight against ISIS as a war or as a counterterrorism exercise, as President Barack Obama termed the matter in his prime-time address last Wednesday.
"This isn't [about] talking points, but [it's] very serious business," McDonough told ABC "This Week" host Martha Raddatz. "We believe just as we have been at war with al Qaida since the day we got here, here we are at war with ISIL."
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On NBC, Todd pointed out that in his interview last week with the president, he asked if he was preparing the country for war, and Obama insisted it is not a war.
"You asked if he was preparing the country for war," McDonough said. "He was preparing for this against ISIL. There was no debate between the White House and [the] Pentagon. inasmuch as we have been at war with Al Qaeda, we are at war with ISIL."
The discussion also included Saturday's news that the insurgents had beheaded British aid worker David Haines, in retaliation for British leader David Cameron entering a coalition with the United States against the militants.
The beheading is the third by ISIS in recent weeks, after those of two U.S. journalists, James Foley, 40, and Steven Sotloff, 31, who had been taken as hostages in Syria.
McDonough told Raddatz that he does not have any "particular news or analysis" on who Haines' executioner was, but the United States is doing "everything we can to keep the heat on ISIL."
He also sidestepped Raddatz' questions over whether the British will now join in conducting air strikes against ISIS, saying that the U.S. stands "shoulder to shoulder with our ally and our close friend, the UK," but the situation is still developing.
But as part of the battle, McDonough told Raddatz, that means the United States is going to "use our unique capabilities in support of others on the ground. We'll obviously be supporting the Iraqi security forces and in Syria we'll be supporting with air power the Syrian opposition that's on the ground now."
Meanwhile, the Iraqi troops have been fleeing the advances of ISIL, and McDonough told Raddatz that has been happening because of the "intense sectarian nature of Iraqi politics over the course of the last many years."
As a result, he said, Obama was "very discerning and very prudent in the use of our air power, notwithstanding pressure to do more than he did earlier in the summer," as he wanted to be sure a new prime minister and a multi-ethnic government was in place in Baghdad.
"They will support a unified, capable multi-ethnic Iraqi force so that they can take this fight to ISIL," said McDonough. "Ultimately they need to do it for their success as well as ours."
McDonough said he is not in a position to discuss whether there is a limit on the numbers of troops being sent to Iraq.
"We will be very candid with the American people as the president has been," he said. "We'll work very closely and consult with Congress on this effort, and we believe that we have the right strategy."
The efforts against ISIS are being undertaken with a "broad coalition," McDonough told Todd, but "it's not like the war in Iraq. This is something that is targeted and it's a war we have to win."
McDonough admitted that the international effort won't be easy, and Obama is "going about this in a very painstaking and very prudent fashion" while Secretary of State John Kerry is continuing his efforts to get other nations to join in the fight.
Meanwhile, work is going on to put together support for a Title 10 program to train and equip Syrian opposition, as "we all recognize we need a ground force of Syrians, of a Sunni force fighting ISIL in Syria, the same way we will have Iraqi forces on the ground in Iraq."