Imprisoned former Illinois Gov. Rod Blagojevich asked the U.S. Supreme Court on Tuesday to hear an appeal of his corruption convictions that included his attempt to sell an appointment to President Barack Obama's old Senate seat.

An 83-page filing making the request argues that the line between the legal and illegal trading of political favors has become hopelessly blurred, potentially exposing politicians everywhere to prosecution.

"This case presents an ideal vehicle for providing the needed clarity," it says.

The Supreme Court hears only around 80 cases a year out of more than 10,000 such requests. It typically accepts cases that raise weighty and divisive legal issues, which is why the filing emphasizes what it says are the far-reaching implications of Blagojevich's case.

The 58-year-old Blagojevich is serving a 14-year prison sentence in Colorado. A lower court tossed five of his 18 convictions in July, and he's now asking the Supreme Court to toss the rest.

An appeal to the high court is a last slim hope for Blagojevich, who proclaimed his innocence for years on talk shows, including NBC's "The Apprentice" when Republican presidential candidate Donald Trump still presided over the reality show.

Tuesday's filing says that the high court should state clearly that politicians cross the line into criminality when they enter into an explicit, unambiguous agreement with a donor to take specific official action in exchange for campaign cash.

The lack of such clarify in U.S. law, the filing says, could invite "arbitrary and discriminatory enforcement against politicians like Blagojevich who are outspoken, controversial, polarizing or simply have become unpopular since their election."

Since his 2008 arrest and through his two trials, Blagojevich has argued he was participating in legal, run-of-the-mill politicking.

The 7th U.S. Circuit Court of Appeals also grappled with the issue of what is and isn't corruption when it struck five of Blagojevich's convictions in its July ruling. The three-judge panel determined that Blagojevich crossed that line when he sought money — often campaign cash — for naming someone to the U.S. Senate seat that Obama vacated when he became president. But the judges said he didn't cross it by asking for a Cabinet seat for himself.

The panel concluded that secretly trading favors based on politicians' executive powers was a legitimate way to get things done for constituents.

Using that reasoning, the judges tossed convictions linked to Blagojevich's bid for the Cabinet post in exchange for appointing an Obama adviser to the Senate. But they said evidence on the 13 remaining criminal counts was "overwhelming."

In a modest win for Blagojevich, the panel ordered that he be brought back to Chicago to be resentenced. But it also said his original 14-year sentence might be considered fair even after subtracting the five overturned counts. A resentencing hearing has not yet been set; the 7th Circuit said resentencing should go ahead even if the high court agrees to hear Blagojevich's appeal.