WASHINGTON — Lt. Gen. Robert Neller, the administration's nominee to lead the US Marine Corps, said Thursday that Russia is the "greatest potential threat" to the US, but to the American people, he said the top threat is "radical extremism."

Neller, who appeared before the Senate Armed Services Committee at a July 23 hearing to consider his nomination as commandant, said he believed that Russia is nation-state threat, but the threat of violent extremists — he did not mention the Islamic State by name — is of equal concern. Neller did not mention the Islamic State by name.

"I don't think they want to fight us, I don't think they want to kill Americans," Neller said of Russia. "I think violent extremists want to kill us, and their capability is not that great, but their intent is high. The fact that they have a message that seems to resonate around the world, not just in this country, but in other countries in the Western world, they concern me equally."

Neller said of he US Marine Corps participated in a joint and multinational exercise in the Baltics that the Marine Corps participated in: , and Neller said, "I'm sure it was paid close attention by certain countries in that part of the world." The naval warfare exercise, Baltops 2015, included 5,600 troops from 17 nations conducting maritime defense, air interdiction, anti-submarine warfare and amphibious operations.

US President Barack Obama nominated Neller earlier this month to succeed Gen. Joseph Dunford as commandant of the Marine Corps. Dunford, who became commandant in last October, has been was nominated to chair the Joint Chiefs of Staff; a confirmation vote is pending. Neller, the commander of Marine Forces Command in Norfolk, Virginia, has also been nominated for promotion to a fourth star, which he would receive upon becoming commandant.

A chorus of nominees for top US military posts — including Dunford and Gen. Mark Milley, the Army chief of staff nominee — have recently called Russia the greatest security threat to the United States.

Like Dunford, Neller will grapple with an expanded post-Afghanistan operational tempo and the equipping and modernization needs of an active force — all within the confines of shrinking defense budgets.

Frank Hoffman, a senior research fellow at the National Defense University, said Neller will inherits a Marine Corps that is well-postured to respond promptly to the nation's crisis needs, but "needs to continue to hone its readiness for near-term combat and security missions, largely in the Middle East while supporting the US pivot to the Pacific in the longer term."

My take on hisNeller's principal looming challenge is the lack of adequate ground mobility vehicles against modern "hybrid threats,." Hoffman said.

On Thursday, lawmakers questioned Neller about the impact effect of sequestration budget cuts, the service's modernization priorities and the outlook in Iraq, where the US is training Iraqi forces to combat the Islamic State group.

Neller, who served in Iraq's Anbar province for a year in 2007, said he believed Sunni tribes there will fight, if the Iraqi government can convince them. Similar to today, the US then provided training and support with the goal that the Iraqis would own the fight.

"The relation with Sunni tribes is not with us, it's with Baghdad," he said. "They have to believe that the central government will at least give them some modicum of support, fix the roads, give them gasoline, make the electricity work, let them worship as they see fit."

It remains to be seen how effective US actions in support of the Iraqi government will be, he said. Of the Iraqis attempting to gain control of Ramadi, he said. "I believe the Iraqis can do this, I believe they have the capability, if well led and supported — they have the will."

SASC chairman Sen. John McCain, R-Ariz., lost patience toward the end of the hearing, after Neller offered a number of cautious answers. Asked what the US needs to do in Iraq, Neller said, "We're doing what we need to do in Iraq right now," essentially equipping and advising the Iraqis, without accompanying them into battle.

A hot-button issue is whether the military should send joint terminal attack controllers (JTACs), a course that has been was ruled out by the Obama administration. Although Neller conceded maneuver units are typically more effective when they work with JTACs, he stopped there, and his answer — in combination with others — sparked McCain's ire.

"When you say what we need to do in Iraq, I don't know where you've been," McCain said. "The Iraqis have to do it. But without American assistance, including air power and forward air controllers on the ground, we're going to see this stalemate. For you to say, 'We're doing what we need to do,' well, maybe you can tell me what we're doing that will win against ISIS. Can you tell me that?"

Amid questions from McCain, Neller said ISIS is in a stalemate, triggering a tongue-lashing from McCain, who said he was "very disappointed with some of your answers."

McCain told Neller the two had a "very strong and different view of the situation," and invoked Fallujah and Ramadi, cities where many Marines died in the Iraq war.

"You say to us to say we're doing what we need to do is not in keeping with the appreciation we should have for the sacrifice these brave young people have made," McCain said.

On the F-35B joint strike fighters — the service's short-takeoff, vertical-landing variant of the aircraft — Neller said the service had completed an operational readiness evaluation and was nearing a decision to declare initial operating capability, though that would be left to Dunford to recommend to the defense secretary.

"The real exciting thing" about the plane, Neller said, was its targeting ability and its ability gather and disseminate information.

"I'm an infantry guy," he said. "Planes are nice but they're really nice when they drop bombs and tell me what's on the other side of the hill."

Neller said the service is concerned, as with any new program, about the availability of space parts — but he later professed confidence in the jets, despite their expensive price tag.

"It is expensive, but the more our allies buy, the cheaper it will be. So I'm excited about the potential this provides, not only to the Marine Corps and the naval force, but the joint force."

WNeller named the service's top two ground modernization priorities the Amphibious Combat Vehicle (ACV) and the Joint Light Tactical Vehicle (JLTV), which he characterized as a needed replacement for the Humvee.

On the JLTV, Neller said the service needed a vehicle that was survivable and mobile, and that he assumed the JLTV would meet the requirement as he had not seen any test data.

On the ACV, the Marine Corps had hoped planned to buy a high-speed planing vehicle — the now-cancelled TK — but that became too expensive and unreliable, Neller said. While the service explores such a vehicle, it plans to replace its outdated amphibian tractor with off-the-shelf vehicles for the ACV, nearing a down-select decision this fall.

"Because this vehicle spends 90 percent of the time on shore, we have to find something that can move us around on shore, but get us through the surf and onto the beach" he said.