Team Rubio always expected the Florida senator to begin to peak around this time. The campaign takes a long view of the 2016 nominating contest, a strategy that looked increasingly risky as rivals Sen.
But exit polls show Rubio drew support not only from Iowans who made up their minds in the final days, but also from those looking for a viable candidate who can win in November.
Rubio's backers now call it a three-way race with Cruz and Trump, dismissing the remaining seven main GOP contenders. They see Rubio as the best alternative to the hard-line Texas senator and the billionaire reality star in the battle against the Democratic nominee.
"I think people realize on the Republican side that we cannot afford -- this country cannot afford -- to lose this election, and that I give the party the best chance not just to unify the conservative movement but to grow it," Rubio said Tuesday morning on "Good Morning America." "And defeat Hillary Clinton or Bernie Sanders."
Risks, though, abound. Rubio's optimistic message of a better future, somewhat clouded recently by his fear-stoking outlook on national security, may play well in New Hampshire. After that, the electoral calendar is not on his side.
The Southern states, starting with South Carolina, have strong religious underpinnings that may be more welcoming to Cruz, who pulled more evangelical votes in Iowa than any other candidate, and Trump, who has drawn large crowds. Nevada, the fourth contest, offers some hope for Rubio, who spent part of his childhood there while his dad worked as a casino bartender, but polling has not put him ahead.
Rubio also will need cash to keep his campaign running -- and a suit of steel to handle the incoming attacks from Cruz and others.
In New Hampshire, rivals who share his more tempered conservative approach -- Jeb Bush, Chris Christie,
If Rubio expects to have the resources needed to push on, donors will need to coalesce around his campaign in a way that hasn't yet happened.
While the senator's fourth-quarter fundraising haul was his best yet, Rubio still lags behind the small-donor base that Cruz has inspired, and Trump's ability to dip into his wealth to fund his campaign.
Rubio's team acknowledges the long haul is longer than they expected, but the goal is to build what the campaign calls "Marcomentum" until Florida, his home state, votes March 15, creating an inevitability of his nomination.
He picked up the backing Tuesday of South Carolina Sen.
Conservative Solutions, a super PAC supporting Rubio, began running TV ads nationally and in the early nominating states Tuesday to try to reinforce his inevitability.
"Marco Rubio is the conservative who can win -- and the Clinton machine knows it," said one ad. "Rubio beat the establishment. He'll unite Republicans and restore the American dream."
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