During the debate Bush went after Rubio. Now Rubio's team is going after Bush's donors. | Getty Rubio team goes after Bush donors On conference call with donors, Rubio team urges backers to not attack Bush.

DENVER—For months, Republican donors viewed Marco Rubio as a growth stock. After his bull run in Wednesday’s debate, investors are buying.

It started even before the debate in Boulder ended. Donors who had been getting calls from Rubio’s Colorado campaign chairman for two months were suddenly emailing him. Seven donors he’d been working couldn’t convey their messages fast enough: I’m in.


“The movement in donors and activists is significant and palpable,” said Josh Penry. “People saw Marco last night and they saw a conservative and they saw a winner. The people who always liked him but doubted his polish now see a guy on stage they can see next to Hillary Clinton.”

What Penry felt in Colorado was happening nationwide. In the hours after the debate, Rubio’s campaign saw its online fundraising numbers skyrocket.

As of 3 p.m. Thursday, Rubio had raised $750,000 in online contributions from more than 14,000 unique donations, according to a top campaign official. Rubio wasn’t the only one to see a boost – competitor Ted Cruz, who scored one of the most talked-about lines in the debate, raised $772,000, and even more quickly, his team said.

But for Rubio, the influx of donors marks a gain against rival Jeb Bush in a feud for establishment money that has been simmering for weeks.

Rubio aides Todd Harris and Anna Rogers held a conference call with Rubio’s financial backers on Thursday, and told them not to expect a massive immediate rush of defections among Bush’s donor base. There are heavy emotions involved when people make a switch like this, Harris said, and the campaign shouldn’t expect folks to just turn on a dime.

But big donors seem ready to move, according to some Rubio backers. Penry declined to discuss specific Colorado donors, although one of the biggest gets in the state, Larry Mizel, appears to be on board.

“Phones have been ringing off the hook all day,” the campaign official said. “Fundraisers already scheduled are seeing increased attendance—and lots of people want to host events."

Mizel, a Sheldon Adelson confidante and member of his Republican Jewish Coalition, met with Rubio earlier this week, spent Wednesday afternoon in the spin room and watched the debate in person. Thursday morning, he walked into the Brown Palace Hotel downtown for a Rubio fundraiser (a make-up for a previously postponed event) carrying a check.

“He likes to keep his name out of it and work behind the scenes, but he’s with Marco,” said a source close to Mizel.

Liberty Media CEO Greg Maffei, the most sought after Colorado Republican donor who remains uncommitted to a candidate, was also in the audience to see Rubio’s debate and his devastating counter-punch that leveled Jeb Bush. But Maffei, who bought six tickets to the debate and brought along his main political adviser, has yet to tip to his associates if he’s any closer to putting his support behind Rubio or any GOP presidential hopeful.

While Wednesday night’s debate may turn out to be a major turning point in the nomination fight, the moment when big money donors shift from Bush to Rubio, the senator’s campaign team knows that they have a lot of work to do to catch up to Bush’s organizational strength.

Bush’s camp knows it too. His brother warned against predicting the end of Bush’s campaign. “Four years ago Perry and Cain were fighting for the lead,” former President George W. Bush told a gathering of White House alumni in Washington, according to an attendee. “It’s too early to rely on polls. Jeb will be fine.”

Plus, Rubio’s team is eager to avoid fueling what could be seen as a petty fight with an old, and still respected friend.

"Be respectful of Marco's relationship with Jeb," Harris said, according to one person familiar with what was said on the call, urging Rubio's supporters to not attack Bush after the former governor’s lackluster debate performance. He reminded those on the call that Rubio and Bush had a long relationship that predated the current contest.

Harris and a Rubio spokesman, Alex Conant, declined to comment on the finance call.

“The general feeling is that we had a very good night, but still have a lot of work ahead of us,” said a campaign official. “It was one of many debates, and we have another in less than two weeks. We have over three months to go before the first contests—we're staying focused on executing our strategy with the goal of being first in February.”

Alex Isenstadt contributed to this story.