Donald Trump during an interview with Business Insider. Sam Rega/Business Insider Donald Trump looked up from his desk and, at the end of a 45-minute interview, sounded as if he had talked himself into it.

"I'm going to win, I think," he told Business Insider.

Five months after Trump officially entered the presidential race, that possibility is beginning to set in for a wide swath of the Republican establishment — and the political-pundit class — that long assumed Trump would fade from front-running status.

In fact, Trump remains on top, and the only one seriously challenging his dominating standing in the polls is another so-called outsider candidate: retired neurosurgeon Ben Carson.

After seven months of campaigning and four debates, the Republican presidential primary is a virtual "free-for-all," party strategists and political analysts say. Trump and Carson have climbed to the top. The original establishment front-runner, former Gov. Jeb Bush of Florida, has faded. Upstart Sens. Ted Cruz of Texas and Marco Rubio of Florida have risen, but it's unclear whether they can rally enough support from the party's different wings.

Overall, there's a prevailing sense that numerous candidates in the robust 15-candidate field could capture the nomination.

"We're definitely going to have a free-for-all over the next few weeks," said Erick Erickson, a prominent conservative radio host who is editor-in-chief of the blog RedState.

"That seems about right to me," said Liz Mair, a political strategist and former aide to the short-lived campaign of Gov. Scott Walker of Wisconsin, when asked about the free-for-all sense.

The fourth GOP presidential debate, run last Tuesday by Fox Business Network and The Wall Street Journal, did little to change that underlying dynamic. The consensus held that Cruz and Rubio continued to solidify their rising positions, that Trump and Carson did little to alter their current status, and that Bush staved off some of the bleeding from a haphazard debate performance two weeks earlier.

Meanwhile, former Hewlett-Packard CEO Carly Fiorina delivered strong moments that resonated with conservative viewers. Sen. Rand Paul of Kentucky finally broke through with a pointed critique of Trump, and his campaign told Business Insider that fund-raising had "picked up" over the past few days.

And Gov. Chris Christie of New Jersey, who failed to even make the main stage on Tuesday night, has seemingly gained momentum over the past couple of weeks, fueled by a steady performance at the lower-tier debate Tuesday.

"There are a lot of bends in the river to go," argued Chip Englander, Paul's campaign manager.

"Voters are just beginning to tune in," he added, "and Senator Paul wins them over when they learn about his 14.5% flat tax and that he's the only candidate with a plan to balance the budget by eliminating hundreds of billions of dollars and abolishing cabinet departments."

Trump and Ben Carson. AP Photo/Morry Gash

The race is unsettled enough, however, that a significant bunch of the Republican establishment is beginning to worry about the possibility of Trump or Carson grabbing the nomination.

The success of the pair thus far has flummoxed and flustered fellow GOP rivals, who have openly question how a reality-television star has foiled years, and sometimes decades, of their preparations for the nation's top job.

"On our side, you got the number-two guy — tried to kill somebody at 14," Sen. Lindsey Graham of South Carolina said recently, referring to a story from Carson's memoir, "Gifted Hands," that recounted a youthful violent streak. "And the number-one guy is high energy and crazy as hell. How am I losing to these people?"

And despite Rubio's rise, there has been no consensus establishment alternative to come into view. Bush, with his allied super PAC, still has the most resources of anyone in the field — but he has been unable to latch on as a candidate.

It has gotten to a point at which The Washington Post reported on Thursday that, again, supporters of 2012 GOP nominee Mitt Romney had begun plotting a strategy for a late entry into the race. For his part, Romney has continually insisted that he will not jump into the field after mulling a third run earlier this year.

"It doesn't surprise me," one veteran GOP strategist told Business Insider when asked about the Romney speculation. "Everything is still very unsettled."

"The Romney boomlet is awesome," Erickson, the conservative radio host, added. "Cruz can really capitalize on this, and it reads like a damning indictment of Rubio. Rubio is the guy the Romney people should love."

Ted Cruz, left, and Marco Rubio. REUTERS/James Lawler Duggan

In fact, a materializing sense of harmony is starting to form about the eventualities of the race: Rubio and Cruz are looking increasingly likely to be the last two men standing in the crowded field — at least according to those who doubt the long-term viability of Trump and Carson. Both Rubio and Carson have shone in each of the four debates, rising steadily in national and early-state polls.

And each of the two candidates appears to be increasingly aware of the threat posed by the other. A simmering feud on immigration this week burst out into the open, with each candidate sniping at the other's respective position on the issue. The pair's advisers engaged in a furious air war over Twitter — and in reporters' inboxes — to press their cases.

"We're watching the emergence of two genuine stars, Rubio and Cruz, in a political process that rewards fresh faces," said Greg Valliere, the chief global strategist at Horizon Investments. "The focus increasingly will shift to issues, a potential mine field for front-runners Carson and Trump."

But judging from Trump's and Carson's post-debate activity, you wouldn't know it.

They have been engaged in an increasingly nasty feud, with Trump trying furiously to knock Carson down while Carson has continued to face questions about stories from his personal background. On Thursday night, Trump used an approximately 95-minute speech to tear into Carson in every way imaginable, comparing his "pathological" temper to the supposedly "incurable" behavior of child molesters.

Trump's outburst Thursday night caused some in the party, again, to predict the end.

Then again, even as Graham predicted Trump's demise, he acknowledged this: "I've said that before."