Jonathan Burkan, a financial services executive who was supporting Mr. Walker, said he received his campaign news from multiple media sources, in what he calls the C.I.A. model. “I look at a bunch of things, and if they’re all saying the same thing, that concerns me,” he said. “That makes me nervous.”

And there are the polls, perhaps most critical in stirring up donor anxieties. “It’s all numbers,” said Eric Anton, a New York real estate executive who was a Walker bundler. “A lot of analytical banker types are donors, so they track that like they track the stock market.”

As handling concerns from contributors has become a crucial job for campaigns and super PACs, many have devoted at least one person, in part, to donor maintenance. Austin Barbour, a senior adviser to the super PAC that supported former Gov. Rick Perry of Texas, said he would regularly receive a flurry of calls from worried donors — “What’s the plan? What are you putting on TV? Why are you doing that? Why are you not saying this?”

But Mr. Barbour, who is now joining Mr. Bush’s campaign, said he was happy to field the complaints: “If they wanted to talk to me for an hour, I’d talk to them for an hour,” he said. “They were the ones who were funding what we were doing, so goodness gracious, the least thing I could do is answer whatever questions they had.”

In addition to the more traditional donor maintenance — like holding regular conference calls between the donors and top campaign officials and sending thank-you notes — campaigns are finding innovative ways to make donors feel involved.

The campaign of Senator Marco Rubio of Florida has provided his financial backers with a password-protected mobile app that provides updates on the candidate, details of his schedule and even helpful talking points.