(CNN)Marco Rubio's third-place finish in Iowa positioned him to seize the mantle of the Republican establishment, but the crowd of mainstream GOP rivals who have staked their campaigns on the next contest in New Hampshire aren't making it easy.
Establishment 2016ers aim fire on Rubio in New Hampshire
With so much riding on the Granite State -- where Jeb Bush, Chris Christie, and John Kasich are counting on strong showings -- attacks on Rubio have escalated.
On Wednesday, the Bush campaign hammered Rubio with a full-page ad in the New Hampshire Union Leader, an influential newspaper in the state, that featured a letter "from the people who know Marco and Jeb best" -- former and current speakers of the Florida House of Representatives (a position Rubio formerly held).
The seven Florida leaders who signed onto the letter praised Bush's record as governor of the state and warned against nominating Rubio.
"While Senator Rubio is a tremendous political talent, he is not the best choice to serve as Commander-in-Chief," they wrote, adding, "Take it from the people who know Marco and Jeb best. Governor Bush is the leader we need to make America safe, stronger, and freer."
Other establishment rivals depending on New Hampshire have also taken aim at the ascendant senator from Florida, seeking to blunt his momentum out of Iowa.
In an lengthy conversation with reporters at his New Hampshire campaign headquarters on Tuesday, Chris Christie ripped Rubio for his lack of experience, his political polish, and what he sees as soft treatment from the media, calling him "the boy in the bubble."
"Let's get the boy in the bubble out of the bubble and let's see him play for the next week in New Hampshire. I'm ready to play. I hope he is because I'll be ready to see him on stage on Saturday night," Christie said.
"It's time for him to man up and step up and stop letting all of his handlers write his speeches and handle him, because that's what they do, that's what you have to do for somebody has never done anything in their life," Christie said.
And in a conference call with reporters Tuesday, Kasich campaign aide John Weaver sought to contrast his candidate's executive experience with Rubio's senate record, unfavorably comparing the freshman to Obama.
"The governor has a record, Senator Rubio does not," Weaver argued. "If past is prologue in government and politics and life, voters are looking for some certainty, and that's -- particularly compared to what we've had with President (Barack) Obama, who had a similarly record-free political life before he became president."