Newt Gingrich’s financial problems and his fourth-place finish in the Illinois primary Tuesday underscore his serious challenges going forward in his bid for the Republican presidential nomination.

Gingrich’s campaign reported that it was $1.6 million in debt at the end of February, compared with $1.5 million it held in the bank, according to campaign filings released Tuesday night. At the end of 2011 and in January, Gingrich had more money in the bank than he had debt, but in the most recent report he was back in the red overall.

With 8 percent of the Illinois vote, Gingrich finished behind Rep. Ron Paul (Tex.), who had held only one campaign event in the state this year, compared with six for Gingrich.

Gingrich has won 135 delegates of the 1,140 delegates needed to secure the nomination. That compares with 563 for Mitt Romney and 263 for Rick Santorum, according to Associated Press totals.

Gingrich campaign spokesman R.C. Hammond said the former House speaker would stay in the race all the way to the Republican convention.

“We have a strong base of donors who are still committed to stopping Mitt Romney and going to Tampa,” Hammond said.

The main super PAC backing Gingrich, Winning Our Future, reported that it had $2.3 million in the bank at the end of February but has spent just $120,000 on ads backing him since March 6, the date of the Super Tuesday contests.

The new financial documents show that Gingrich continued to raise money through February in the run-up to Super Tuesday. But he won just one contest that day, his home state of Georgia, and went on to lose two Southern states, Mississippi and Alabama, on March 13.

Gingrich’s campaign has had a rocky path. Early on, he was dogged with the revelation that he had a $500,000 line of credit at Tiffany. In June, most of Gingrich’s senior staff resigned en masse in protest of his management style.

But he surged to the top in national polls before the Iowa caucuses, only to lose there to Santorum amid heavy negative advertising by Romney and his backers. Gingrich handily won South Carolina but lost in Florida 10 days later.

To an extent, Gingrich is in a better position financially because of his considerable personal wealth. His various businesses have generated more than $100 million in revenue in the past decade, and he has reported more than $6 million in assets, with $2.5 million in income over 2010 and part of 2011.

Financial problems often propel candidates to drop out of the running, including former Minnesota governor Tim Pawlenty, who ended his GOP bid in debt. Pawlenty endorsed Romney, who went on to help his new surrogate pay down the debt. But a similar arrangement between Romney and Gingrich is unlikely, given the bitter ex­changes between the two.

Gingrich’s current debt is owed to a mix of campaign vendors and staff members. The biggest creditor is Campaign Fundraising Experts LLC, a Mesa, Ariz., firm that is owed $122,651.

The campaign appears to be paying off some vendors while accumulating debt to others. Gingrich paid off $200,000 of a $271,000 bill to Moby Dick airways for charter jet use. But the campaign incurred a $119,000 debt to the firm of his longtime lawyer, Randy Evans.

The campaign reported $3,840 in debt to Angel de la Portilla, an Orlando political consultant who ran the campaign’s Hispanic outreach in Florida. Portilla said in an interview that he sent an invoice to the campaign for $6,000 after the Florida primary Jan. 31. He followed up with a phone call at the beginning of this month, and staffers said it would take three more weeks to get paid. After sending an e-mail Monday, he was told checks would be cut Wednesday, he said.

Originally, “they told me it would take about 30 days,” de la Portilla said. “Obviously if it drags on longer, I’ll be concerned.”

One group of people who have not been paid quickly are the staff members who resigned from the Gingrich campaign in June. Former campaign manager Dave Carney’s firm is owed $20,617 and former spokesman Rick Tyler has been owed $1,667 since June.

Tyler went on to help found the Winning Our Future super PAC, which has spent $17 million to boost Gingrich. Tyler did not return a request for comment.

A former senior staff member said Gingrich may be staying in the race for personal reasons.

“I suspect he’s having a ball,” said the staff member, who commented on the condition of anonymity to speak candidly. “Newt’s one of those guys where if he’s in the news it’s a good day, regardless of why he’s in the mix.”