Speaking at his Senate Armed Services Committee confirmation hearing, Nicholson said that the plan for an long-term U.S. military commitment was part of the President's policy shift that allowed for the retention of 5,500 troops beyond his presidency.
While Obama had originally sought to withdraw all U.S. troops save for a small embassy presence, in October the President revised the draw-down plan to keep thousands of troops in Afghanistan into 2017.
Nicholson was responding to a question as to whether he envisioned a U.S. commitment to Afghanistan resembling the decades-long deployment of U.S. military forces in Germany and South Korea.
Currently, the 9,800 U.S. troops stationed in Afghanistan are split between the NATO-led training and assist mission, Operation Resolute Support, and a separate mission tasked with performing counterterrorism operations.
Nicholson said it was clear that "trans-national terrorist organizations," including ISIS and al Qaeda, were attempting to "establish sanctuary inside Afghanistan."
Earlier this month, U.S. forces in Afghanistan were granted the authority to directly target ISIS in Afghanistan, also known as ISIS-Khorasan or ISIS-K, as part of its counterterrorism mission.
Nicholson recognized that the emergence of ISIS-K in 2015 and the continued presence of al Qaeda in Kandahar province meant that the counterterrorism mission had expanded in recent years, potentially requiring an increase in U.S. counterterrorism capabilities.
Nicholson also acknowledged that the coalition's end of combat operations combined with a "shortfall in Afghan air power" had contributed to a lack of air support for the Afghan army's campaign against the Taliban. He said the Afghan air capability would take a long time to develop and that the U.S.-led coalition needed to address this gap in the interim.
Senator Lindsey Graham, a South Carolina Republican, pressed Nicholson on whether there could be a combat role for US troops in the face of a major Taliban military victory, to which Nicholson responded that U.S. troops would not sit on the sidelines.
Libya a growing concern
Separately, Secretary of Defense Ash Carter canceled a planned trip in order to attend a National Security Council meeting at the White House Thursday to discuss a U.S. plan for countering ISIS's growing presence in Libya, according to several administration officials.
Libya is now "the area of most growing concern," when it comes to ISIS, a senior defense official told CNN.
Carter told reporters that ISIS is consolidating its presence in Libya and "part of its ideology is to attack Westerners, including Americans."
He noted that the Libyan branch of ISIS was showing the "same kind of ambitions" that it had shown in Iraq and Syria, and that it was setting up training installations, attracting foreign fighters, and seeking to control the local economy.
One U.S. official familiar with the latest intelligence said that it's estimated some 500 ISIS personnel may have traveled to Libya in the last months of 2015. And in many cases, ISIS handlers are now redirecting recruits who show up in Turkey to Libya instead because of the difficulty in crossing the border into Syria.
Carter said the U.S. is focusing first on trying to support the political process in Libya in hopes a government can be installed. If that happens, the U.S. military can then work with that government to conduct air, and possibly ground, operations against ISIS targets.
The Pentagon considers it essential to have some friendly elements on the ground in Libya that would support a U.S. effort before it could conduct ground operations in any substantial manner, the officials said.
But there is also an understanding that ISIS might have to be dealt with sooner, due to its rapid expansion. To that end, the U.S. is planning on stepping up overhead reconnaissance and drone operations to begin to pinpoint and strike ISIS targets from the air, officials say.
Carter said that counterterrorism operations, including airstrikes, would continue against ISIS in Libya, with or without the formation of a unity Libyan government.
The National Security Council consultations also included the latest efforts to expand the war against ISIS in Iraq and Syria. The Pentagon in particular is seeking more contributions from allies of troops for training of Iraqi army and police forces.
Biden puts time stamp on Raqqa push
Meanwhile, Vice President Joe Biden suggested Thursday that the ISIS stronghold of Raqqa and key Iraqi city of Mosul could face the same fate as Ramadi -- an Iraqi city that the Iraqi army recently retook from ISIS -- by "the end of the year."
He was speaking at the House Democratic retreat in Maryland. He said that self-interest was also encouraging other international actors, include Turkey and Europe, to step up.
"The president's finally gotten the attention of the Europeans to pony up, since they haven't been doing much of anything," he said, adding that Turkish President Recep Tayyip Erdogan "has seen the Lord."
Russia, U.S. closer in Syrian skies
Also on Thursday, U.S. and Russian military officials met to discuss their respective air campaigns in Syria, where the U.S. is targeting ISIS and Russia is supporting its ally, President Bashar al-Assad.
Top Pentagon officials held a classified video teleconference with their Russian Ministry of Defense counterparts to discuss measures to ease conflicts regarding Syrian airspace "to avoid accidents and unintended confrontation" between the two sides, a Pentagon spokesman said.
There have been at least two previous bilateral sessions since the Russians began air strikes in Syria last year. This latest round of talks was sparked by several operational changes, according to a senior U.S. defense official.
Both sides are now flying in greater proximity to each other. U.S. aircraft have recently operated near Aleppo in northwestern Syria, where the Russians have long been active, and the Russians have been striking ISIS targets near the eastern city of Deir Ezzor, where the U.S. air campaign has been active.
Additionally, both sides now have forces on the ground. The U.S. does not plan to tell the Russians exactly where U.S. Special Operations forces are located in northern Syria, the official said, but it wants the Russians to be aware generally where the U.S. troops are, as well as where other local forces assisting the U.S. are located.
The meetings are taking place despite the restrictions on U.S.-Russian military cooperation that were put into place following Russian military activity in Crimea and eastern Ukraine.
Other instances of military cooperation between the U.S. and Russia have been criticized by members of Congress.
The chairman of the Senate Armed Services Committee, Arizona Republican Sen. John McCain, slammed the Air Force and Department of Defense Wednesday for continuing to rely on a space rocket that uses Russian-made engines.
During a committee hearing, McCain charged that the use of Russian RD-180 rocket engines meant that the U.S. is "giving tens of millions of dollars to corrupt oligarchs." McCain also said the Russian company that manufactures the engines is overseen by board members that were placed under sanctions in the wake of the Russian armed annexation of Crimea in 2014.
"They are a bunch of thugs and cronies of Vladimir Putin, some of them are ex-KGB," McCain told CNN's Wolf Blitzer, referring to the board members in question.
