A pair of senators sparred Sunday over President Obama’s approach to Islamic extremism in the Middle East, highlighting the difficult task facing the administration, as it tries to strike a balance between its military and diplomatic response to the rising threat.

{mosads}Sen. Ron Johnson (R-Wis.), who voted Thursday in favor of granting Obama new powers to train Syrian rebels fighting the Islamic State in Iraq and Syria (ISIS), said he’s open to “doing what it takes” to defeat the terrorist group. But he suggested Obama’s plan, while a start, is not aggressive enough.

“You cannot negotiate with ISIS. Their diplomacy consists of beheadings [and] crucifixions,” Johnson said on NBC’s “Meet the Press.” “I’m extremely open to doing what it takes to achieve the goal that President Obama has stated. We have to defeat ISIS.”

Sen. Chris Murphy (D-Conn.), who voted against the train-and-arm proposal, said he’s wary of that approach because the “so-called moderate rebels have been openly coordinating” with al Qaeda. He suggested Obama’s plan to help those rebels could enmesh the United States in another prolonged conflict in the Middle East.

“It’s likely an impossibility that they can effectively fight on two fronts against both Assad and against ISIS,” Murphy said. “To me, the risk is that the United States begins getting involved in what may be a very long-term commitment to a messy civil war inside Syria.”

Murphy said he’s “broadly supportive” of Obama’s plan, but “the question is whether getting involved in a very complicated, sectarian civil war in Syria is necessary to the overall strategy.”

Murphy advocated for airstrikes in Syria and a stronger focus on Iraq, which, he said, would “effectively degrade ISIS to the point that you have the room for a political solution.”

“We totally misunderstand how you beat a group like [ISIS],” he said of Congress.

But Johnson said the diplomatic approach is simply not realistic, suggesting Obama’s plan won’t achieve the president’s goal “to degrade and defeat” the ISIS militants.

“I agree with President Obama’s goal that they must be defeated,” Johnson said. “I’m just not seeing the strategy that’s actually going to work.”

The White House is pushing a multi-faceted approach to combating ISIS that includes targeted airstrikes, the building of an international coalition to confront the group and humanitarian aid to those affected by the violence.

Last week, Congress provided another element of the plan, when it gave Obama new powers to train the Syrian rebels outside of Syria.

Both Johnson and Murphy said Sunday that they’re agreed on one element of the debate: The commitment from Islamic countries is so far insufficient to the task.

“They aren’t as committed as the United States. Saudi Arabia is not leading this coalition, the United States is leading this coalition,” Murphy said. “And that really is going to be the key as to whether this is ultimately successful.”

On Wednesday, Obama will address the United Nations General Assembly in New York City in an attempt to broaden that international commitment.