Jeb Bush's Fall (or Maybe Rise)

—PORTSMOUTH, NH -- On the eve of today’s New Hampshire presidential primary, Republican presidential candidate Jeb Bush finished his day at the Frank Jones Center on the seacoast, the same locale where another unlikely GOP contender, John McCain, once hosted his final town hall in a state that he ultimately won eight years ago.

The former Florida governor joked that "the Bushes are getting acclimated" to New Hampshire again after his mother visited days ago, nodding to the state in which the family has collectively won four primaries.

He then became reflective.

"I've done 100 events, more or less, town hall settings, in people's homes, in some of the most iconic diners I've ever seen in my life," Bush said. "Now we're getting to the end of this and I just want to say thank you because ... it's been an extraordinary experience to listen and to learn."

Many, including some of Bush’s own advisers, believe New Hampshire is his final stand, his last opportunity to prove to the Republican establishment and his powerful donor base that he is a viable candidate who has a shot in future primaries.

Some of his backers fear tonight could be the end of the line. But it’s just as plausible that New Hampshire could be the beginning of Bush's second wind.

Bush has seen a rise in some polls and has seen his campaign recharged by a solid debate performance and an uptick in crowd size.

It’s no secret that the Bush campaign has gone all-in here. Supporters were shipped in from Florida to door-knock, make calls and plant yard signs around the Granite State. An analysis of voter contact, conducted by Monmouth University polling director Patrick Murray, found that Bush led the Republican pack in outreach.

But for donors, though the campaign and super PAC's money may be abundant, time is not.

"I have a great respect for voters in New Hampshire, probably as astute as any voters anywhere,” one Houston-based donor told ABC News. "You can get a fairly good sense of what's important when we see how New Hampshire votes.”

He, like many others, believes Bush must beat the other two governors in the race -- John Kasich and Chris Christie -- in order to continue.

"You have to look at who's in your lane, whether he wins or hangs even, is it a death knell? Not at all, but it's very important to show strength in his lane," said the donor, who declined to be identified in order to speak candidly about expectations for Bush.

Another Washington-based donor told ABC News, "Don't count Jeb out."

Bush's team is cautiously optimistic, hoping for a top-tier finish that can propel them into South Carolina, a state many within his team refer to as "Bush Country."

But, first, he'll have to stave off Kasich and contend with his former protégé, Marco Rubio, who has been grappling with a poorly reviewed performance in the final presidential debate before the primary.

Sandy Stowe, a retired teacher who lives in Portsmouth, braved a snowy night to see Bush at his final event of the day.

"Rubio was my guy before the debate,” she said, “but the debate showed me that Rubio is less experienced.”

When asked whether the Florida senator could still be president, she said, "In a few years.”

Moments earlier, surrounded by an enthusiastic crowd, buoyed by the many staffers and supporters that came in from Florida, Bush made his final appeal.

"You’re from New Hampshire, you can change the course of anything. ...If you don’t think the pundits are right, the obituaries written about all the candidates including me, that it’s all done, it’s all figured out; if you disagree with that, you can reset this race tomorrow," he said Monday, adding, "You have that power. No one else does, no one else does. It’s an extraordinary responsibility.”

When Stowe, the retired teacher, was asked whether she believed Bush still had a chance, her eyes lit up.

"I think he does, yeah!” she said. “Anything can happen.”