Federal prosecutors have described Illinois Gov. Rod Blagojevich's alleged scheme to sell Barack Obama's former U.S. senate seat to the highest bidder as abject, blatant corruption.
But, for the senate candidates seeking to fill the vacant seat, the case touches on a murky area between accepted political favor trading and illegal conduct.
The controversy over the seat has embroiled Congressman Jesse Jackson Jr., who emerged Wednesday as one of several candidates allegedly mentioned by Blagojevich in conversations recorded by the FBI as someone the governor apparently thought would pay money to be appointed to the senate.
"There are gray areas when you say, 'Hey I'll be supportive of you, I'll vote for your bill if you vote for mine. If I'm elected, I'll support your initiatives.' That's politics," said Ron Safer, the former head of the criminal division of the U.S. Attorney's Office in Chicago.
"I will pay you $500,000 for the Senate seat, that's black and white," he said. "It's black, dark black. 'Appoint me and I'll get a fundraiser together and I guarantee you you'll get $1 million' -- that's bribery."
Jackson, the son of civil rights leader the Rev. Jesse Jackson, has denied any wrongdoing. He has not been accused of any misconduct and said he has been told by prosecutors that he is not a target of the investigation.
A certain amount of goodwill is implied in any political appointment, said Chris Lehane, a Democratic strategist and former staffer in the Clinton White House.
"There is an implicit understanding in a situation where you're making an appointment, particularly a U.S. Senate seat, that the person you select is going to appreciate that and will reflect a degree of loyalty going forward," he said.
"But it's not something you ever explicitly have a conversation about," he said. "The reality is there is a bright shiny line that you just don't go over."
Others who work in politics were not as sure that the line is that bright. "Is it wrong to say I want this job and by the way I'll raise money for you and the party, I'll help your candidates? That's the normal course of politics," said New York political consultant Hank Sheinkopf.
"It depends on the timing and the real intent. It's one thing to raise money for a political campaign, it's a different thing to say I'll give you money for personal use."
Jackson, identified as Senate Candidate 5 in the investigation , might face criminal charges if prosecutors can prove he authorized one of his associates to offer money in exchange for Barack Obama's Senate seat, former federal prosecutors say.
But, any agreement about the senate seat would need to go beyond normal political horse-trading in order to be criminal, attorneys say.
"There's horse-trading that's accepted practice," said Patrick Collins, a former federal prosecutor who successfully prosecuted former Illinois Gov. George Ryan. "Perhaps one line is whether there is a personal benefit attached to the demand on both sides. What makes it potentially corrupt is, appoint me and I'll get you some cash in return."
Political consultants said the kind of alleged quid pro quo arrangement described in the Blagojevich case is unusual.
"People raise a lot of money for them and then they appoint those people. That happens all the time," said Tad Devine, a senior advisor to Al Gore and John Kerry in their presidential campaigns.
"But when you get down to sort of quid pro quo, putting money attached to to it, you're really getting into a dicey area," he said. "There's implied consent as opposed to express consent. People don't sit and wheel and deal dollar amounts in exchange for jobs."
According to the Blagojevich affidavit, on Dec. 4 Blagojevich allegedly told an adviser that he might "get some [money] up front, maybe" from Candidate 5, if he named him to the Senate seat.
In a recorded conversation on Oct. 31, Blagojevich allegedly claimed he was approached by an associate of Candidate 5. "We were approached 'pay to play.' That, you know, he'd raise 500 grand. An emissary came. Then the other guy would raise a million, if I made him [Candidate 5] a senator," Blagojevich said, according to the affidavit.
The Chicago Tribune, citing unnamed sources, reported today that businessmen with ties to Blagojevich and Jackson Jr. discussed raising at least $1 million for Blagojevich's campaign as a way to encourage him to pick Jackson for the Senate seat.
In order to charge Jackson, prosecutors would need to show that Blagojevich's statements are true and that Jackson directed or authorized a representative to approach the governor and offer money in exchange for the Senate seat -- "two huge hurdles the government would have to overcome," said Safer.
Blagojevich and his chief of staff were charged in a criminal complaint with conspiracy to commit mail and wire fraud and solicitation of bribery. They have not yet been indicted; if and when they are, prosecutors may provide more details of their alleged crimes.
None of the candidates has been accused of a crime.
"There is a prosecutorial path both for the governor's side of the equation and for any Senate candidate who was corruptly offering money for the Senate seat," said Collins. He and other attorneys said such candidates could face fraud and conspiracy charges.
A lawyer for Jackson Jr. told ABC News' The Blotter on Wednesday that Jackson was the person identified in court papers as Candidate 5 but said "Jackson has never authorized anyone to seek the Governor's support in return of money, fundraising or other things of value."
Attorneys who spoke to ABC News said they expected U.S. Attorney Patrick Fitzgerald's office would pressure Jackson's alleged emissary, if that person exists, to cooperate with the investigation.
"I think they'll absolutely pursue that emissary from Candidate 5," Safer said.
"The next step is anybody who thinks they may have some culpability is going to be running with their lawyers to Fitzgerald's office to broker some sort of a deal," said James Cohen, a professor at Fordham Law School. "This is really just the beginning."