OKATIE, S.C. (AP) — The best hope of the Republican establishment just a week ago, Marco Rubio suddenly faces a path to his party's presidential nomination that could require a brokered national convention. 

That's according to Rubio's campaign manager, Terry Sullivan, who told The Associated Press that this week's disappointing performance in New Hampshire will extend the Republican nomination fight for another three months, if not longer. It's a worst-case scenario for Rubio and many Republican officials alike who hoped to avoid a prolonged and painful nomination fight in 2016.

"We very easily could be looking at May — or the convention," Sullivan said as Rubio's charter jet traveled from New Hampshire to South Carolina this week. "I would be surprised if it's not May or the convention."

The public embrace of a possible brokered convention marks a sharp shift in rhetoric from Rubio's top adviser that could be designed to raise alarm bells among Republican officials. Yet days after a disappointing fifth-place finish in New Hampshire and looking up at Donald Trump in next-up South Carolina, Rubio's presidential ambitions are truly facing growing odds.

"After this week I feel 55," the 44-year-old senator joked as he courted voters at an Okatie elderly community Thursday.

The joke aside, the first-term Florida senator discussed his political challenges at length during an unusual 45-minute question-and-answer session with reporters aboard his campaign plane the day before. He answered questions until there weren't any more, noting afterward that he hadn't held a session that long with reporters since his days as Florida's House speaker.

In remarks that were at times personal and others defiant, he also may have simply needed to talk it out to help process his predicament. It also seemed he needed to prove to the political world, himself and his family that he could face the biggest test of his young presidential bid.

"My kids were watching me last night," Rubio said of his nationally televised admission that a poor debate performance pushed voters away. "My kids knew that it didn't go the way I wanted it to go."

"I taught them more last night from that experience, I feel, than any words I'll share. They were learning from that experience," he said.

As he shifts his attention to South Carolina's Feb. 20 contest, Rubio wants voters to know he's learned an important lesson from his experience in New Hampshire. Instead of trying to avoid attacking his GOP rivals on the debate stage, Rubio said he's now prepared to fight back when necessary — particularly with his party's front-runner Donald Trump.

A more aggressive Rubio showed up Thursday in Okatie.

"Donald Trump has zero foreign policy experience — negotiating a hotel deal in another country is not foreign policy experience," he charged, adding similar jabs at former Florida Gov. Jeb Bush and Texas Sen. Ted Cruz.

"I will never ask you to be angry at another group of Americans in order to win an election," he added in a clear reference to Trump.

New Hampshire destroyed any momentum Rubio had coming out of Iowa and for now, at least, locks the senator into a messy muddle in his party's establishment wing. Both Ohio Gov. John Kasich and Bush beat Rubio in New Hampshire in the contest to emerge as the mainstream alternative to Trump and Cruz.

And as senior aides embraced the possibility of a brokered national convention, Rep. Trey Gowdy, R-S.C., said the Rubio operation is "built for a long campaign."

"I don't know of anyone who expected folks to fold up after New Hampshire and go on. There are a lot of candidates," Gowdy said as he was traveling with Rubio on Wednesday. "He's never indicated to me anything other than we're built for the long haul and it's going to be a long haul. But, you're running to be the leader of the free world — it's supposed to be a challenge."

And while he called on his party to unite behind his candidacy Thursday in South Carolina, Rubio seemed to offer a broad definition of "quickly."

"If we don't' come together quickly, we can't win," he said. "If we are still fighting with each other in August, and September and October, we won't win."

The Republican Party holds its presidential nominating convention in July.

There hasn't been a contested convention since 1976, yet Republican National Committee officials have already had preliminary discussions about the possibility of no candidate securing a majority of delegates in the state-by-state primary contests in the coming months.

It's by no means assured that Rubio's candidacy will survive that long.

Despite his popularity among many Republican leaders, he will ultimately need to start winning primary contests to remain competitive — especially as Trump and Cruz perform well.

Sensing weakness, Democrats and Republicans alike have begun to question Rubio's long-term viability. But the mood was encouraging inside a packed Okatie rally on Thursday.

"He had a bad moment. They all have bad moments," said Barbara O'Connor, 67, a registered Republican.

"I loved that he took responsibility," she continued. "I hope he wins."