WASHINGTON - Politicians make deals every day. They do favors and ask them in return. They kowtow to campaign contributors. It may be unsavory, but it's often perfectly legal.

The prosecutors who arrested Illinois Gov. Rod R. Blagojevich say his conduct went far beyond politics as usual into a pattern of corruption. Where's the line?

There's a vast gray area in which political deal-making flourishes. President-elect Barack Obama acknowledged as much yesterday, speaking of wheelers and dealers who ask, "What's in it for me?"

Joseph diGenova, a former prosecutor, said political corruption can be a bit like obscenity - hard to describe, but "you know it when you see it." He said it's especially hard to prove criminal behavior involving campaign contributions, as opposed to personal enrichment.

"It's not like, 'Gimme $50,000 in a black bag and I'll give you the nomination,' " he said. "People give campaign contributions and expect things in exchange. It's all perfectly legal."

Prosecutor Patrick Fitzgerald, announcing the criminal complaint against Blagojevich, said he wasn't "trying to criminalize people making political horse trades on policies or that sort of thing. But it is criminal when people are doing it for their personal enrichment."

The line is crossed, diGenova said, when an official act is paid for with money or something else of value. Some of the proposed deal-making by Blagojevich in his taped conversations might make people gasp but isn't necessarily criminal.

"A lot of these issues do fall into a gray area, where it may be hard to distinguish between politics as usual - practices that go on in statehouses all over the country - and criminal conduct," defense attorney Ross Garber said.

Taking money in exchange for official government action is clearly illegal. But it may be just savvy politics when a governor names his rival to be a state judge so she won't oppose him next election.

What about when Hillary Rodham Clinton endorses Barack Obama, who helps pay off her campaign debt and then names her secretary of state? No allegations of a crime there.

In the Blagojevich case, he allegedly states that "I want to make money." If it's proven that he tried to sell a Senate seat for personal gain, that's clearly illegal.

Former New York Gov. Mario Cuomo said Blagojevich's situation was more a case of "politics as absurd" than politics as usual. "Normally, there is subtlety in these attempts at self-serving," he said, "but here there was no subtlety."