MANCHESTER, N.H. >> In the crowded New Hampshire primary, no candidate may shape the direction of the Republican presidential campaign more than the man who finished sixth in Iowa: Jeb Bush.

With Sen. Ted Cruz of Texas, Donald Trump and Sen. Marco Rubio of Florida each finishing more than 20 percentage points higher than Bush in the Iowa caucuses Monday, the former Florida governor is facing growing pressure to either demonstrate his appeal to voters or leave the race.

Specifically, many Republicans — including some of his supporters and donors — said Tuesday that Bush must finish ahead of Rubio in the primary here on Feb. 9 to justify continuing his campaign into South Carolina.

“If Rubio beats him badly in New Hampshire, Jeb is toast,” said Sen. Lindsey Graham, R-S.C., a Bush backer who spent most of Tuesday traveling the state with him. Graham added that Bush must either “tie Rubio or beat him” in this state.

The burden falls so heavily on Bush, who won just 2.8 percent of the vote in Iowa, because of Republican anxieties about the top two finishers there, Cruz and Trump: Many party leaders fear that the nomination of Trump or Cruz would lead to an electoral rout this fall.

Were Bush to continue his campaign into South Carolina, he could create a split among pragmatic-minded voters, denying Rubio the chance to consolidate this bloc of Republicans — and strengthening the hands of Cruz and Trump. Many Republicans believe that if Rubio, who won an unexpected 23 percent in Iowa and closely trailed Trump, again delivers a strong performance in New Hampshire, he will have earned the right to carry the banner for the party establishment.

Asked Tuesday evening by reporters how well he felt he needed to do in New Hampshire to justify continuing his campaign, Bush struck a defiant note.

“Oh, I’m continuing on,” he said. “I’m continuing on, yeah.”

Two other candidates, Gov. Chris Christie of New Jersey and Gov. John R. Kasich of Ohio, are appealing to the same voters and also need a strong showing in New Hampshire. But Bush is far better financed and organized and can most likely stay in the race longer than they can otherwise.

While Bush had $7.6 million in the bank and the super PAC supporting him had an additional $58.6 million as of Jan. 1, Kasich had just $2.5 million and Christie a paltry $1.1 million. And neither Christie nor Kasich, both of whom have spent the vast majority of their time in New Hampshire, has much in the way of organization in South Carolina.

Bush, by contrast, has an active network of supporters there and has tapped into Graham’s organization. And perhaps most important, the super PAC supporting Bush has shown a willingness, to put it mildly, to spend millions of dollars against his rivals, particularly Rubio, whom it has spent more than $20 million attacking.

The prospect of the super PAC continuing its assault on Rubio after the New Hampshire primary leaves many Republicans uneasy about Bush’s intentions. And Rubio’s supporters, cognizant of these concerns, began moving Tuesday to stoke these fears.

“If Jeb doesn’t do well there, and he’s still got millions and millions to spend, does he stay around?” mused Sen. Cory Gardner of Colorado, a Rubio backer. “Who knows.”

But, Gardner noted ruefully, “more money has been spent attacking Republicans by fellow Republicans in this election than any cycle in the history of the party.”

It is not just supporters of Rubio who are dismayed. Some of Bush’s major donors, including those with long ties to the family, are also growing impatient, hoping he will not go past New Hampshire absent a strong finish here.

Few are willing to say so publicly, and on a Tuesday conference call the campaign held for fundraisers, they did not even get a chance to say so privately: The Bush aides running the call did not open it up to questions.

It is unclear what threshold Bush might feel he must reach to continue his campaign after the New Hampshire vote. But on the conference call and in talking points the campaign emailed late Monday night to supporters, Bush’s team pointed to surveys showing him in a statistical tie for second place in New Hampshire.

The campaign also built up Bush’s effort to win the state, noting how many times he had visited, and trumpeted New Hampshire’s recent role in determining the Republican standard-bearer. (Left unmentioned was the 2000 primary, in which George W. Bush, Bush’s older brother, suffered a landslide loss here and still went on to claim the nomination.)

“The Granite State has long been the state voters look to in choosing the nominee and next president,” the staff wrote in the memo, highlighting Jeb Bush’s endorsements and organizational strength.

In reality, Bush’s top advisers know Rubio’s finish in Iowa makes it harder for Bush to claim he is the logical alternative to Trump and Cruz. Yet he seems torn between focusing his fire on Rubio or Trump.

On Tuesday, his campaign began airing an unusually long 2-minute ad in New Hampshire attacking Trump for insulting veterans, women and the disabled. And at a stop in Henniker, N.H., Bush aimed some of his most pointed language yet at Trump, who finished second in Iowa, calling him a “loser” with “deep insecurities.”

Yet on the same day Bush went so aggressively after Trump, he also sought to raise doubts about Rubio, incorporating Cruz for purposes of comparison.

“If you look at their records, they’re gifted in how they speak, but what about their life experience?” Bush asked the crowd at Franklin Pierce University in Rindge, N.H., likening the two senators to President Barack Obama, who was elected president after less than four years in the Senate. “Is there something in their past that would suggest they have the capability of making a tough decision?”

Yet there are signs Bush may still have some work to do to finish in the top tier here. Speaking to a crowd at the Hanover Inn near the Vermont border during his final stop of the day, Bush finished a fiery riff about protecting the country as commander in chief — “I won’t be out here blowharding, talking a big game without backing it up,” he said — and was met with total silence.

“Please clap,” he said, sounding defeated.

The crowd laughed — and then, finally, clapped.