The days of Florida Sen. Marco Rubio flying under the radar may be coming to an end.
For months, the Republican White House hopeful was content to keep a low profile while he built his campaign and his rivals attacked one another. Now, the Rubio camp is working hard to translate momentum from a well-received debate performance Wednesday into a much-needed fundraising boost and expansion of his base of support, while the candidate barnstorms in Iowa over the weekend.
“Sen. Rubio has put himself in a position to organically pick up [former Florida Gov. Jeb] Bush voters, just like he put himself in a position to pick up [Wisconsin Gov. Scott] Walker’s voters,” said Iowa state Sen. Rick Bertrand, a Rubio supporter.
Eager to pounce on Bush donors after an underwhelming debate performance by the onetime front-runner, Mr. Rubio’s super PAC advisers circulated a memo Friday making the case that just four Republicans can win the nomination at this point: Mr. Rubio, retired neurosurgeon Ben Carson, celebrity businessman Donald Trump and Texas Sen. Ted Cruz.
On Friday, billionaire hedge-fund manager and major GOP donor Paul Singer sent a letter to his network of donors announcing that he had decided to support Mr. Rubio, the senator disclosed at an event in Iowa. Mr. Singer met with Mr. Rubio last week. The move is a major blow to Mr. Bush and other Republicans who had been vying to win Mr. Singer’s support and could encourage other big donors to get behind Mr. Rubio’s campaign.
“When people donate to us, they buy into our agenda, and I’m glad that he has,” Mr. Rubio said. “I mean, it will help us with resources.”
Mr. Singer’s decision was earlier reported by the New York Times on Friday.
The Rubio campaign’s aggressive posture reflects the sense of shifting momentum since the third GOP debate, which elicited plaudits for Messrs. Rubio and Cruz for their forcefulness, as well as criticism of Mr. Bush.
A key moment came when the Mr. Bush attacked the senator for missing votes in Congress, and Mr. Rubio dismissed that as an act of desperation by his onetime ally in Florida politics. “Someone has convinced you that attacking me is going to help you,” Mr. Rubio shot back.
Robert Brownell, an elected official in Polk County, Iowa, who is helping organize on Mr. Rubio’s behalf, said he has “definitely noticed an uptick in interest—and confidence—in him,” and that was before this past week’s debate.
Rick Christoffers, 60 years old, attended a Rubio event in Sioux City on Friday, even though he objects to Mr. Rubio’s positions on immigration and prefers other candidates. Still, Mr. Christoffers was impressed by him in the debate for the way he took on the son and the brother of presidents. “I like what he said to Bush. He kind of cut him down,” Mr. Christoffers said. “Bush has had a silver spoon in his mouth.”
Mr. Rubio now can expect a more aggressive examination of his résumé. Concerns linger about his personal finances, his experience and his Senate voting record. (Mr. Rubio canceled a campaign event Friday morning to return to Washington and vote against a two-year budget deal.) The Bush campaign recently circulated a memo drawing attention to those issues, dubbing Mr. Rubio a “risky bet.”
One of the knocks against Mr. Rubio is that his bare-bones campaign lacks the infrastructure to compete with better-financed rivals, including the two poll leaders, Messrs. Trump and Carson. The Rubio campaign raised more than $1 million following Wednesday’s debate, according to an aide, after collecting a little more than $5 million during the entire three months that ended in September.
Data remain murky on where candidates are investing their money, but the latest round of campaign-finance reports suggests Mr. Rubio is spending a larger share of his budget in the first four nominating states than many of his Republican rivals. Roughly 20% of the $4.6 million he shelled out between July 1 and the end of September was spent on lodging, rent, consulting fees and events in Iowa, New Hampshire, Nevada or South Carolina.
The Rubio campaign now employs about 70 full-time campaign workers, a 20% increase over the prior month, according to an aide. About half of those people are assigned to the task of organizing teams of volunteers in the early voting states.
Rubio supporters said interest in his campaign has risen in recent weeks, but he and his allies still don’t have enough money to match the Bush forces. Mr. Bush and his allies are sitting on more than $100 million to run television ads promoting the former governor, according to campaign-finance reports. That money translates into roughly $10 million in advertising in Iowa and more than $24 million in New Hampshire, according to figures published Friday in the Cook Political Report by Elizabeth Wilner, head of Kantar Media’s Campaign Media Analysis Group.
Mr. Rubio and a pair of affiliated groups are on a pace to keep up with Mr. Bush and his outside allies in Iowa, but his campaign, super PAC and a nonprofit are now slated to run roughly $7 million in ads in New Hampshire, according to the same Kantar figures.
After raising an unimpressive $5 million in the third quarter, the Rubio campaign has stepped up its efforts to court donors who are still undecided, as well as some who have already contributed money to other candidates.
A fundraiser in Washington later in November boasts more than 50 co-hosts, a staggering show of force for a candidate who has been overshadowed by his rivals on the fundraising circuit this year.
During the past week, top Rubio advisers have been stepping up their pressure on many of Mr. Bush’s biggest fundraisers to jump ship and join team Rubio, according to people familiar with those conversations. At least one Rubio adviser has angered some Bush supporters by demanding they switch sides before the next debate, on Nov. 10, these people said.
“This is not the right way to do it,” one Bush backer said. “It’s not the right time.”