Is there more to Nikki Haley's resignation than first meets the eye? Putting together her past opposition to Trump, her thinly disguised ambition to run for the White House one day and the suddenness of the departure announcement, some Republicans think so.

Nikki Haley declared herself “not a fan” of President Trump two weeks before the 2016 election. Author Michael Wolff branded her "as ambitious as Lucifer." A key Trump ally said Tuesday that the timing of her resignation "raised eyebrows" and "seemed odd."

Haley's 2016 criticism of Trump and her differences with him over Russia policy made her a prime suspect when an anonymous “senior official” announced internal opposition to his agenda in the New York Times. Suspicion was thick enough that Haley, U.S. ambassador to the United Nations, wrote a Sept. 7 op-ed in the Washington Post denying she authored the vow of resistance.

The Axios report that broke the news of her departure from the Trump administration teased that it might be linked to the New York Times article, which triggered a furious search for the identity of "Anonymous," viewed as a traitor by President Trump.

[More: The Top 10 contenders to replace Nikki Haley at the UN]

When Trump and Haley traded sunny compliments in the unusually amicable departure announcement, it seemed, on the face of it, impossible that the culprit could be the former South Carolina governor. If Trump believed that might be the case, most Republicans concluded, he would have summarily dismissed her, perhaps with his trademark slogan: "You're fired!"

But do Trump’s warm words for Haley exclude her from the list of possible authors? “No,” said longtime Trump adviser Roger Stone flatly. “The president, who I love and support, does many things I don’t understand.”

Stone, who previously floated the possibility that nobody wrote the anonymous op-ed, said Trump doesn’t always act in a way that he would expect.

“Take for example his decision not to fire John Dean — I mean Rod Rosenstein,” Stone said, mischievously comparing the former White House attorney who helped undermine President Richard Nixon to the current deputy attorney general. Stone's conduct is under review by special counsel Robert Mueller, whose work is supervised by Rosenstein.

Haley announced her resignation Tuesday, about a month after the anonymous op-ed posted. A resignation letter was dated Oct. 3, though the decision was not made public until shortly before a rare Oval Office send-off.

Former Trump campaign aide Sam Nunberg, who Trump fired twice, said he would have expected a more aggressive dismissal if Haley was suspected of writing the op-ed. Nunberg said he believes that Haley was resigning to serve her future career interests, at Trump’s political expense.

“She should have waited until after the elections, and you do this the day after Kavanaugh?" he said. "Nikki is all about Nikki."

Nunberg said he doubts Haley was “stupid enough” to write the anonymous op-ed, however, because “if she comes out and says 'I was the author of it', they are going to say, 'Why didn't you come out and criticize the president earlier? Why did you do it anonymously?'”

At the same time, he added: “What I do think is that it was highly suspect that she issued a denial of it in a piece in the Washington Post.”

Trump’s decision to host Haley in the Oval Office and swap compliments sharply contrasts with other recent departures. In March, Trump announced on Twitter that former Secretary of State Rex Tillerson was fired. White House chief of staff John Kelly later denied Tillerson was fired on Twitter. Instead, Kelly told reporters in leaked off-record remarks, he fired the nation’s top diplomat over the phone while Tillerson was sitting on an African toilet, suffering from diarrhea.

American Conservative Union Chairman Matt Schlapp, a well-connected Washington Republican and staunch Trump backer who is married to Mercedes Schlapp, White House director of strategic communications. suggested on Fox News, as the news was breaking Tuesday morning, that there might be more to the story.

"Unless this is a personal issue or health concern, which I hope is not the case, it's obviously very unusual for a significant and prominent person on the president's team to announce that she is leaving so close to an election. There is something to this story. Like everyone in America I want to know what it is,” Schlapp said on TV.

As of Tuesday afternoon, Schlapp told the Washington Examiner that he had no new information to flesh out his suspicion, and that he had no reason to believe it's related to misconduct, such as a role in the op-ed or allegedly improper use of private flights, raised this week by a Democratic-leaning watchdog group.

“I haven’t learned anything that makes it any more complicated than the knowledge out there,” he said. “All I can determine is that the facts are as they are describing them."

“The timing of it raised eyebrows,” Schlapp said. "The timing for a lot of people seemed odd, right on the heels of this great celebration about the confirmation of Brett Kavanaugh, but putting myself in their shoes perhaps Nikki Haley was kind enough to say, 'Get through that fight first'.”

"I don't know why they decided to make it public today," he said. "It could be as simple as that's what they agreed to do. It might be he wanted to make sure she was serious."

Haley attributed her decision simply to a desire to move on after about two years in the demanding job. She did not announce her next career move, other than to deny she would challenge Trump in 2020.

Sean Spicer, former White House press secretary, said he "never thought" Haley was the anonymous author. “She has a done a great job as U.N. ambassador and any attempt to paint her as anything but effective and loyal is ridiculous," he said.

Former White House foreign policy adviser Sebastian Gorka was even more blunt, telling the Washington Examiner: "Anyone who ever [posited] Nikki being the author of the New York Times piece was smoking something that’s not tobacco."