President Donald Trump and Secretary of State Rex Tillerson during a bilateral meeting. AP Photo/Alex Brandon As a candidate for president, Donald Trump toned down President Barack Obama's call for Bashar al-Assad to step down, saying the Syrian president was fighting ISIS, a mutual enemy of the United States.

But following Assad's use of chemical weapons against Syrian rebels last week, Trump's administration appears torn over how far to go with its Syria policy — with some members of the administration explicitly calling for Assad's removal from power.

Though the administration last month said removing Assad was not a top priority, some key figures on Sunday telegraphed their renewed support for removing the Syrian president.

In an interview on "State of the Union," the US ambassador to the United Nations, Nikki Haley, didn't directly answer whether the administration supported regime change. But she said that there couldn't be a resolution to the conflict where Assad remains in power.

"Getting Assad out is not the only priority," she said on Sunday. "And so what we're trying to do is obviously defeat ISIS. Secondly, we don't see a peaceful Syria with Assad in there.

"Regime change is something that we think is going to happen because all of the parties are going to see that Assad is not the leader that needs to be taking place for Syria. So what I think you're seeing is, this isn't about policy or not, this is about thoughts. And so when you look at the thoughts, there is no political solution that any of us can see with Assad at the lead."

White House national security adviser H.R. McMaster told Fox News he also supported removing Assad, but said the US was "not going to be the ones who effect that change."

"Other countries have to ask themselves some hard questions," he said on Sunday. "Russia should ask themselves, 'What are we doing here? Why are we supporting this murderous regime that is committing mass murder of its own population and using the most heinous weapons available?'"

UN ambassador Nikki Haley. AP Photo/Mary Altaffer

Others were more hesitant to strike a new tone, despite Trump's decision to strike a Syrian airfield used by Assad.

Secretary of State Rex Tillerson told ABC that there was no change in US policy from last month.

"We've seen what that looks like when you undertake a violent regime change in Libya, and the situation in Libya continues to be very chaotic, and I would argue that the life of the Libyan people is not all that well off today," Tillerson said Sunday. "So I think we have to learn the lessons of the past and learn the lessons of what went wrong in Libya when you choose that pathway of regime change."

"Any time you go in and have a violent change at the top, it is very difficult to create the conditions for stability longer term," he added.

Who represents Trump's view?

The contradictory sentiments garnered criticism from top lawmakers, who were left to infer which policymaker represented the president's thinking.

Sen. Marco Rubio on Sunday said that Tillerson's strategy was "based on assumptions that aren't going to work."

"There seems to be a difference between what Ambassador Haley is saying, as she said last night, that Assad really has no future, and what I heard this morning from Secretary Tillerson," Rubio said on "This Week."

He added: "There is no such thing as 'Assad yes, but ISIS, no.' This theory that you can defeat ISIS as long as Assad is there is not true. They're two sides of the same coin."

Democratic Sen. Edward Markey told CNN that Haley was advocating for forcefully removing Assad from power using US troops.

"It means doing in Syria what we did in Iraq in removing Saddam Hussein," Markey said. "I don't think there's any appetite in the United States for a massive additional military presence, with young men and women actually in combat situations being introduced."

Differing foreign policy mindsets emerge

Trump shakes hands with National Security Adviser and former Army Lt. Gen. H.R. McMaster. Thomson Reuters

The contradictions represent the diverging foreign policy power structures that have emerged within the Trump administration.

Despite reportedly turning down offers to serve as Trump's secretary of state, Haley has emerged as the administration's top spokesperson on foreign policy issues.

While Tillerson and his State Department have largely shunned the press, Haley has sat down with the major television programs, and delivered speeches to the UN that cable news channels carried live. She's also reassured key allies, and been more outspoken in criticizing Russia than her Washington counterpart, who has a longstanding relationship with Russian President Vladimir Putin.

Politico reported last week that Haley may be poised to inherit the job from Tillerson later in the administration.

McMaster, too, has consolidated power within the National Security Council by demoting allies of former national security adviser Michael Flynn. This week, Trump's top political strategist Steve Bannon was removed from the principals committee, while deputy national security adviser KT McFarland also appeared poised to step down.