Florida Governor Ron DeSantis is striving to deliver an upset in the Iowa Republican caucus in January, a make-or-break moment that could doom or extend his presidential prospects.

With his polling average in the state lagging former President Donald Trump by as much as 30 percentage points, DeSantis is moving more staffers to Iowa, deepening his plan to visit all 99 counties. David Polyansky, DeSantis’s deputy campaign manager, and national political director Sam Cooper were among aides who moved to Iowa this week.

“If Donald Trump is allowed to steam-roll through Iowa, it’s going to be that much more difficult to keep him from winning the nomination,” Polyansky said in an interview. “Look at the behavior and spending of the combined pro-Trump effort. Today, Iowa is where they’re spending, and Ron DeSantis is who they are spending it against.”

The top three polling candidates — Trump, DeSantis and former Ambassador to the United Nations Nikki Haley — are in Iowa this weekend, seeking to pick up supporters of South Carolina Senator Tim Scott, who dropped out of the race Sunday. DeSantis’s campaign said Friday it gained 10 endorsements in South Carolina from previous Scott supporters.

DeSantis and Iowa Governor Kim Reynolds, who endorsed him over Trump, signaled they’re counting on undecided voters.

“What you’ve seen is there’s a lot of people that haven’t made firm decisions yet” in Iowa, DeSantis told reporters Saturday at the opening of his new Iowa campaign headquarters outside Des Moines.

“Iowa breaks late,” said Reynolds. “There’s a lot of time left.”

Trump will hold a rally in Iowa later Saturday, while DeSantis and Haley spoke Friday at an event hosted by Bob Vander Plaats, who leads an Iowa-based Christian group.

DeSantis, who needs a strong showing at the Jan. 15 caucus to be a viable candidate, is concentrating its efforts in Iowa. Reynolds’ recent endorsement is likely to help with voters, though it isn’t reflected in polling yet.

Polyansky acknowledged it’ll be difficult to beat Trump, while citing signs that the former president’s team sees the challenge posed by DeSantis. Trump’s campaign spent $2.5 million on anti-DeSantis ads in recent weeks, and has increased the number of appearances in the state as DeSantis has focused campaigning in Iowa, he said.

“I just don’t know how any candidate can come in and spend millions of dollars to have success in the Iowa caucus yet don’t meaningfully invest it on the ground, that’s just not how you win here,” Polyansky said.

“Now, if there’s somebody that can probably get away with it, it’s Donald Trump and we recognize that,” he said.

Read more: Trump Steps Up Iowa Push, Looking to Lock Up Nomination Early

DeSantis will be using Reynolds’ endorsement to reach out to voters. She’ll campaign with him, and a new ad running in the state features her.

It’ll be important for Iowa’s caucus voters to “hear from Governor Reynolds on the ‘why’ behind her endorsement,” Polyansky said.