For the GOP establishment, Donald Trump's populist campaign is a non-starter. And Ted Cruz is loathed by the GOP party elite in Washington -- something he's happy to tout on the trail.
That leaves Rubio, and raises the stakes for New Hampshire, where he will aggressively argue he is the only viable alternative to Trump and Cruz and can unite the party unlike his more divisive rivals.
First, he needs to convince the party establishment to unite behind him. Campaign officials immediately began making the case that this is a three-person race and that the governors competing with him in New Hampshire -- John Kasich, Jeb Bush and Chris Christie -- cannot win.
Rubio beat fairly low expectations for him in Iowa, while the other three governors barely showed any life in the Hawkeye State. And he will pick up a major endorsement: South Carolina Sen. Tim Scott.
Rubio's team is expecting to become a big target after Monday night -- so much it has already decided to pare back on spending in South Carolina and put that money back on the air in New Hampshire. They will be up to $5.2 million in ad spending in New Hampshire to date after their new $100,000 investment.
"This is the moment they said would never happen," Rubio told supporters Monday evening. "For months, they told us we had no chance."
Aides to both Trump and Ted Cruz now concede that Rubio will have some momentum in the state.
"Rubio is now going to be a play in New Hampshire. Trump is going to have to fend him off now," said one staffer for Trump, who leads most New Hampshire polls significantly.
In some ways, Cruz's victory complicates Rubio's path to the nomination. The hope was for Cruz to end up in second place, something that would have been detrimental to his campaign and could have marked the beginning of the end for the Texas Republican. But with Cruz still in the race, it makes things a bit more challenging for Rubio.
That's because Rubio and Cruz compete for a lot of the same voters. And if Rubio ends up behind Cruz in New Hampshire, that could give Cruz even more life heading into South Carolina and then into SEC primary states. Increasingly, Rubio is looking at Nevada as his first state that could give him a victory.
Bush's welcome mat
Bush is already in New Hampshire, and the man who has viciously attacked his fellow Floridian is not ready to go down without a fight. Speaking of Rubio and Cruz Monday night, Bush said they don't have the experience to win.
"And the two other candidates that are likely to emerge in Iowa are two people that are backbenchers that have never done anything of consequence in their life," Bush said. "They're gifted beyond belief. They can give a great speech. But I think it's time for us to recognize that maybe what we need is someone who can lead."