This story has been updated.

PORTSMOUTH, N.H. -- Rarely does the fate of a scandal-plagued lawmaker matter much in the race for the White House. But Frank Guinta isn't like most other congressmen.

The New Hampshire Republican won his seat last November -- his second stint in Congress after winning in 2010, then losing in 2012. He represents the Granite State's 1st Congressional District, a region packed with would-be voters in this state's first-in-the-nation primary. Given the competitive nature of Guinta's district, he's more familiar than most with the state's political terrain and where to find potential support.

So it's no surprise that an otherwise rank-and-file congressman has earned outsized support and attention from potential Republican presidential contenders.

Former Florida Gov. Jeb Bush, former Texas Gov. Rick Perry, business executives Donald Trump and Carly Fiorina -- even Republicans who took a pass on the race like former ambassador John Bolton -- have donated thousands of dollars or spent time campaigning for Guinta.

"I’ve talked to most, I think just about all of the potential presidential candidates either over the phone or in person," Guinta said in an interview with The Washington Post in March. "I’m happy to give advice and guidance as potential candidates inquire."

At the time, he credited Bush for his support and said that other potential presidential candidates had offered to help. "We’ll certainly take up those offers to help," he said.

But now, Guinta is politically radioactive.

The controversy dates back to Guinta's first congressional run in 2010, when he reported loaning himself $355,000 and amended financial disclosure forms to include a new bank account. Guinta denied accusations by opponents of wrongdoing, and denied accusations that the money came from his parents in the form of illegal campaign donations. But the Federal Election Commission has ruled that he broke campaign rules and will need to refund the money.

Fellow Republicans, including Sen. Kelly Ayotte (R-N.H.), are calling on him to resign. After hearing from Guinta on Monday night, the state GOP said it wouldn't take any official action -- but also didn't explicitly express support for him. Even House Speaker John A. Boehner (R-Ohio) stopped short of defending Guinta on Tuesday when asked about the scandal.

Among presidential contenders, Bush has been most generous by far. He donated $5,200 through his super PAC, Right to Rise, in February. The donations to Guinta were announced on the same day he gave four-figure sums to other Republican lawmakers from New Hampshire, Iowa and South Carolina. He's made dozens of donations to other GOP politicians in the months since. Bush also headlined a fundraiser for Guinta during a whirlwind tour of New Hampshire in March.

Bush also personally donated $1,000 to Guinta's campaign last October. Filings with the Federal Elections Commission show that Bush listed himself as a "self-employed" giver from Coral Gables, Fla. when he made the donation on Oct. 14.

Trump also personally donated $1,000, according to campaign finance records. Perry's RICKPAC gave Guinta $2,500 on Oct. 15. And a super PAC for Bolton, who announced last week that he won't run for president, forked over $5,000 last September.

No other potential candidate appears to have given Guinta money in the past year, according to a review of campaign finance records. But others have donated their time. Fiorina campaigned for him last fall and appeared at a Capitol Hill reception when he was sworn in in January.

Guinta has apologized to constituents and fellow Republicans but is so far rebuffing calls for his resignation.

"I recognize the difficulty of this situation, and to all those expressing their concerns and frustration, I apologize," he wrote in a message to supporters published on his campaign Web site.

If Guinta goes, former Rep. Carol Shea-Porter (D-N.H.), who's now lost to Guinta twice, is expected to run again, according to state Democrats.

The GOP primary would be especially competitive and brutal. Names in the mix include Chris Sununu, a member of the New Hampshire Executive Council, who's also the son of former Gov. John Sununu; Dan Innis, who lost in a primary to Guinta and is the state GOP finance chairman; and Bill Binnie, an investment banker and founder of the NH1 Network.

Asked whether they are standing by Guinta, aides to Perry and Fiorina didn't return requests for comment on Tuesday. A spokesman for Trump said their camp only learned about his troubles from the Post, but said: "We wish him well."

Kristy Campbell, a Bush spokeswoman, said in an e-mail Wednesday that "Governor Bush does not believe Congressman Guinta's actions were appropriate. It is incumbent on public servants to be transparent and ethical. Governor Bush believes the decision on whether or not to remain in the House is up to Congressman Guinta, and ultimately to his constituents."

Bush is scheduled to visit New Hampshire on Wednesday and Thursday. Perry, Fiorina and others will be here soon. Given the rough-and-tumble nature of New Hampshire politics, no doubt they'll be asked soon about Guinta.

Researcher Alice Crites contributed to this report.