A record-breaking fundraising spree by Barack Obama has seen him make 30 separate visits to wealthy donors since April, according to a Guardian investigation into campaign finance trips that are running at more than twice the rate of the president's two-term predecessors.

Although unable to run again for election himself, Obama is estimated to have raised up to $40m for other Democrats since his last inauguration in January as he devotes a growing portion of the second term to financing efforts aimed at winning back control of Congress in next year's midterm elections.

Travelling to the 30 fundraisers, mostly held in private mansions and luxury hotels across 10 cities, has also required him to clock up more than 20,000 miles on Air Force One at an estimated cost to the US taxpayer of more than $6m.

In contrast, the Guardian research reveals presidents of both parties previously averaged only 13 fundraisers in the equivalent period of their second terms. George W Bush attended just 11 similar events, Bill Clinton managed 18 and Ronald Reagan only 10.

The data was collated from 2013 White House pool reports, new research assisted by the Clinton and Reagan presidential libraries, and a tally of the Bush years collated by veteran CBS reporter Mark Knoller.

Donors typically pay up to a legal limit of $32,400 to attend private dinners and drinks receptions with the president, usually in the home of a wealthy benefactor. Party officials declined to disclose overall totals raised in this way, but ticket prices and numbers of attendees are often revealed at the time, indicating a maximum of $41m may have been gathered through Obama's presence since April, according to Guardian estimates.

The money has been split roughly evenly between the Democratic congressional campaign committee (DCCC), the Democratic senatorial campaign committee (DSCC), and the Democratic national committee (DNC), which supports a mix of party campaigns.

Last Friday, for example, Obama, after attending a public event in New Orleans, flew to Miami to attend three fundraisers for the DNC and the DSCC. These included a speech beside the palm trees and swimming pool of wealthy Cuban American businessman Jose Mas Santos, and another poolside event to support Florida senator Bill Nelson. On Thursday, Obama flies to Philadelphia for his 31st fundraiser of the year, also for the DSCC.

Democratic party officials defended Obama's fundraising spree, and blamed Republican intransigence in Congress for driving it.

"House Republicans' reckless and irresponsible agenda is not only driving their approval ratings to record lows – it's boosting our fundraising to record highs," said DCCC spokeswoman Emily Bittner.

"President Obama has been a tremendous asset in DCCC fundraising this cycle, and that's because our donors want to make sure that he has a partner in Congress who will work with him to solve problems, instead of blocking commonsense solutions for purely partisan political reasons."

Campaign finance experts say the unprecedented burst of presidential solicitation during a non-election year reveals how fundraising has become a dangerously permanent feature of modern political life.

Second terms were once a respite from the need to seek re-election finance, but are increasingly dominated by party fundraising in the first and second years, followed by a search for donations toward presidential libraries in the final two years of office.

Jessica Levinson, a campaign finance researcher at Loyola Law School who has studied the growing influence of wealthy donors, says recent efforts in the supreme court to remove campaign finance limits for individuals are likely to exacerbate the trend.

"The downside of all this time spent away from office is the time the president is not doing his job as chief executive, promoting legislation or working with Congress," she said.

"As more money is dropped into the political process it has become a self-perpetuating cycle, requiring politicians to spend ever more time seeking donations rather than governing. It's an imperfect use of his time."

Obama has been heavily criticised in recent weeks for not paying enough attention to crises such as the launch of his flagship health insurance website or the surveillance activities of the National Security Agency, and several of the trips have clashed with key moments in both sagas.

But the office of president also provides enviable logistical support for such efforts, allowing Obama to travel, for example, from Washington to fundraising events in both Boston and Miami and back on one day in June. Using Air Force One is required for security reasons and often justified by other public speaking engagements on the same trip, but every hour in the air costs $180,000.

"Every president does this," said Kathy Kiely of the Sunlight Foundation, a Washington transparency group. "But it's pretty obvious that a lot of these public speaking events are tacked on to provide an excuse for him to be in town."

While his public speaking engagements provide ordinary voters with little more than a handshake opportunity, many of the 3,200 people in attendance at Obama's 30 private fundraising events this year often get one-on-one time with the most powerful elected official in the world.

"He's not out there meeting ordinary people. He's out there listening to the views of those who can afford to give him lots of money," added Levinson. "Over time, this is bound to have a distorting affect on your views of the world."

Obama's fundraisers have included trips to the homes of the heirs to the Getty and Levi Strauss fortunes, four fund managers, Dallas trial lawyers and film producer Harvey Weinstein.

Kiely says Obama has also been active in backing political action committees, known as Super Pacs, that support causes aligned to Democrats running for office.

A recent book on the the 2012 campaign by journalist Mark Halperin alleges that Obama has violated campaign finance pledges by continuing to raise money for Super Pacs.

The White House declined three requests for comment on the Guardian's fundraising findings.

But in broad comments to reporters last Monday, spokesman Jay Carney downplayed the administration's focus on the 2014 midterms when asked by reporters about future support for Super Pacs last Monday.

"I just promise that in November of 2013, I haven't had a single conversation about 2014," Carney told reporters. "I'll indulge you and get back to you to the extent we have answers on these questions, but I can assure you that we won't be spending a lot of time on them in the near future."

In private, the president is unapologetic about the importance of paying to secure control of the House of Representatives, which is currently blocking most of his second-term political objectives.

"If we can get a critical mass in the Senate and folks like that in the House then the sky is the limit. Nothing can stop us," Obama told a group in Atlanta on May 19.

In fact, Obama has been unusually blunt with donors, according to the various pool reports from White House journalists that were used to help collate the Guardian analysis.

"I've run my last campaign, [but] being friends with a politician is like perpetually having a kid in college," said Obama in Los Angeles on June 7 at the home of former News Corp president Peter Chernin. "Every so often, you got to write this big check. And you're trying to figure out where is this money going. Now, the good news is: I'm about to graduate. I can't say the same for the rest of these elected officials here."

The same joke was repeated over cocktails at the Chicago Hilton on May 29.

The pool reports afford an unique glimpse into the fundraising process, which is normally hidden from view during other campaign finance stops.

The May fundraiser in Weinstein's five-storey townhouse in New York, for example, attracted celebrities including Justin Timberlake and Tommy Hilfiger. Other Hollywood notables including Walt Disney chairman Bob Iger, producers Haim Saban and JJ Abrams, pianist Mike Lombardo and actress Katie McGrath were also spotted at the lunch in Chernin's Los Angeles garden in June.

"Sadly, this will get worse before it gets better," said Jessica Levinson. "In the end, it is only public outrage that may stop this never-ending need to keep raising money."