Former House speaker Newt Gingrich leaves after a closed-door meeting in March with Republican presidential candidate Donald Trump in Washington. (Jose Luis Magana/AP)

As Newt Gingrich vies for the chance to be Donald Trump’s running mate, he is still dealing with a financial mess left over from his ill-fated presidential run four years ago.

The former House speaker’s 2012 campaign committee owes more than $4 million to about 100 vendors, including firms that provided charter flights, event planning, public relations and security services.

Gingrich is required to submit a debt repayment plan to the Federal Election Commission by Aug. 1 as part of a settlement he negotiated with the agency in the wake of a complaint that he used campaign re­sources to promote his books.

Although the FEC’s top lawyer found evidence of potential election law violations, the evenly divided commission ultimately deadlocked on whether the complaint merited an investigation, finding only that he failed to properly report a debt.

Still, the charges echo a long pattern of leveraging political stature for personal financial gain that has characterized the career of the 73-year-old speaker-turned-pundit. That reputation, combined with Gingrich’s lingering campaign debt, could make for an awkward fit on the ticket as Trump seeks to capi­tal­ize on voter anger at the political elite and blast “crooked” Hillary Clinton for how she and former president Bill Clinton have made money.

Former House speaker Newt Gingrich is on Republican presidential candidate Donald Trump's short list of potential vice presidential candidates. Here's what you need to know about him. (Sarah Parnass,Danielle Kunitz,Osman Malik/The Washington Post)

Neither Gingrich nor a Trump campaign spokeswoman responded to requests for comment about how Gingrich’s personal and campaign finances­ might play into his chances to be Trump’s vice-presidential nominee.

After two decades in Congress, Gingrich did not follow the revolving-door tradition of lobbying after he left office in 1999. But his business empire relied on selling access to his celebrity, political insights and policy expertise, generating close to $100 million in revenue in the decade after he left office, his attorney has said.

Among the ventures: a for-profit think tank that lured members with promises of “access to Newt Gingrich” and “direct Newt interaction.”

Like the Clintons, Gingrich has been active on the paid lecture circuit, earning as much as $60,000 per appearance, according to his speaker’s bureau posting. At one point, he was delivering 50 to 80 paid speeches a year, he recalled in 2012. As recently as last weekend, Gingrich spoke in Paris at the annual gathering of a controversial Iranian resistance group just days after campaigning with Trump in Ohio, although he did not respond to a question about whether he was paid for the appearance.

Trump has said he is vetting Gingrich, along with Indiana Gov. Mike Pence, New Jersey Gov. Chris Christie and several others, and will make up his mind by late this week. He has relied increasingly on Gingrich throughout the campaign for advice, and told supporters last week that whether or not he picks the former speaker to join the ticket, “in one form or another, Newt Gingrich is going to be involved with our government.”

If the former Georgia congressman is tapped to be on the ticket, the campaign would probably have to contend with questions about Gingrich’s finances.

Speaking at a rally in Cincinnati, Ohio, Republican presidential candidate Donald Trump said that former House speaker Newt Gingrich "is going to be involved with our government." Gingrich is on Trump's vice presidential short list, according to campaign associates. (Reuters)

Much of Gingrich’s income comes through Gingrich Productions, a private company run by his wife, Callista, the company’s chief executive. The company, first formed as Gingrich Holdings in 1999, now serves as the hub of the couple’s professional activities. It sells and promotes their books and documentaries, and offers the former speaker’s “strategic planning, consulting, and training” services, according to the company’s website.

Gingrich’s personal finances became an issue during his 2012 campaign, when his federal personal disclosure form revealed that he owed between $500,000 and $1 million to the jewelry store Tiffany & Co., suggesting a taste for the luxury life. The disclosure reported total assets of at least $7.24 million, while Gingrich also made public a tax return from 2010 showing that he and his wife had made $3.1 million that year.

Gingrich wound down key parts of his business network in the run-up to his 2012 campaign.

In 2011, he sold his majority stake in the Center for Health Transformation, a for-profit think tank that made millions by charging membership fees to corporations and industry groups. The organization went bankrupt not long after, before it was purchased for $20,000 by a Georgia health-care company.

Gingrich’s nonprofit American Solutions for Winning the Future was also dissolved in 2011. It was in debt at the time.

The FEC’s settlement with Gingrich’s 2012 campaign came after the agency’s general counsel found evidence that Gingrich Productions made illegal in-kind corporate contributions to Gingrich’s campaign committee and that the political committee paid for costs related to the company’s activities.

In a 2013 report to the commission unsealed in April, the counsel’s office wrote that Gingrich’s campaign staff and the employees of his production company at times swapped duties as the then-candidate was holding concurrent campaign rallies and book-signing events.

Anthony Herman, then the FEC’s general counsel, wrote that although Gingrich’s attorneys said there was a firewall between the campaign and the company, daily schedules and reimbursement forms showed that the two staffs shared duties.

The review also found that Gingrich’s campaign website included more than 80 links to web pages promoting Gingrich Productions products, book readings and movie screenings.

In all, the general counsel’s office found evidence of seven possible violations of campaign finance laws and sought to open an investigation, the FEC documents show.

But the commission, comprised of three appointees from each party, was evenly split over whether to proceed.

In a statement, the Republican members wrote that the “available evidence indicates that Gingrich Productions went to great lengths” to keep the company’s interests separate from those of the campaign. They added that any value of the links on the campaign’s website to pages promoting Gingrich books and other products was probably minimal and did not merit opening an intrusive investigation.

Gingrich’s campaign was sanctioned for one violation: failing to properly report a $47,005 debt that the campaign owed him personally for the rental of a mailing list.

Gingrich’s former campaign manager, Vince Haley, said in a statement in April that the settlement “represents the conclusion of a thorough examination by the FEC of NEWT 2012’s compliance with federal campaign reporting requirements.”

“At the conclusion of this examination the FEC asked only that NEWT 2012 reword a single entry in its campaign report with respect to an expenditure that had been previously disclosed by the campaign from its first filing, which NEWT 2012 has agreed to do,” Haley added.

As part of the negotiated settlement, Gingrich also agreed to submit a debt settlement plan and shut down his campaign committee, which has barely made a dent in paying down what it has owed vendors since 2012.

The campaign still owes $4.6 million for a wide range of services including travel, legal consulting, fundraising, event production and direct mail. Trump could help pay down that debt if he taps Gingrich as his running mate.

The largest outstanding sum: nearly $1 million owed to the air charter company Moby Dick.

During the campaign, Gingrich assured Moby Dick’s president, Roy Oakley, that he would pay back the debt he owed the company, Oakley told The Washington Post in February 2012.

“I have his personal guarantee that he will repay it whether the campaign is going or not,” Oakley said at the time.

Reached this week, Oakley confirmed that the company was still owed money but declined to comment further.

The campaign also owes $11,250 for event production to the Studio City, Calif.-based Peace River Co., $127,727 to Phoenix-based Gordon C. James Public Relations and $407,620 to Patriot Group, a security services firm in Warrenton, Va. In addition, Gingrich himself is owed nearly $650,000 for travel expenses that the campaign has not yet reimbursed.

Gingrich did not respond to a request for comment on how he plans to repay the campaign debt.

Since the 2012 campaign, Gingrich has worn many hats, including, until recently, as a political contributor to Fox News. On Tuesday, the channel and Gingrich announced a mutual decision to suspend ties, citing the speculation that he could be chosen for the GOP ticket.

Along with the income Gingrich makes from his production company, he is a senior adviser at the law firm Dentons, a senior scientist at the Gallup polling firm, a member of the advisory board of Barrick Gold and a consultant for several health and education companies, he wrote in an email to The Post. As of 2014, one consulting client was the Center for Union Facts, a nonprofit organization that has pushed anti-union measures. The group paid Gingrich Productions $140,000 that year, according to the group’s tax return.

Newt and Callista Gingrich have spent the past four years traveling extensively, documenting their frequent international trips on his active Instagram account.

During his trip to Paris last weekend, Gingrich spoke at an annual gathering for the Mujahadeen-e-Khalq, or MEK, an Iranian group that has pushed to overthrow that nation’s current government, as Buzzfeed first reported. The group was listed as a terrorist organization by the United States until 2012, although it has prominent supporters across the U.S. political spectrum that have long argued its efforts in Iran should be supported.

If Gingrich joins Trump’s ticket, his federal financial disclosure form would be required to list the sponsors of that and other trips if the Gingriches did not pay for them out of their personal funds.

While Trump aides are likely examining Gingrich’s past tax returns as part of the vice-presidential vetting process, it is not clear whether Gingrich or the campaign would feel compelled to release any more of his returns publicly.

Trump, citing ongoing audits by the Internal Revenue Service, has refused to release his tax returns. A decision to keep Gingrich’s tax returns private would probably draw fire from Democrats, as Gingrich in 2012 slammed his then-rival Mitt Romney for being slow to release his own tax returns.

“Either there’s nothing there, so why isn’t he releasing them, or there’s something there, so why is he hiding them?” Gingrich told reporters in the days leading to the 2012 South Carolina primary, which he won. “I believe we have the right to know. Therefore, he owes us the knowledge. If there’s nothing there, why not release it this week?”

Alice Crites and Karen Tumulty contributed to this report.