Judges are usually wary of imposing a harsher sentence after a successful appeal. Unless the judge relies upon new evidence that justifies a longer sentence, an appellate court might presume that the judge imposed more time to retaliate against the defendant for exercising his right to challenge the judge's rulings on appeal.
The linked story does not make clear the government's reasons for recommending a 20 year sentence, and since (as is customary with sentencing documents) the letter containing those recommendations isn't part of the public record, the Justice Department has not commented publicly. According to one of Siegelman's lawyers, the government's recommendation is based in part on a desire to punish Siegelman for crimes that the court of appeals threw out or for which Siegelman was acquitted at trial. Remarkably, judges are allowed to consider acquitted conduct when deciding upon a sentence, although judges who respect the presumption of innocence are loathe to do so.
In any event, the judge obviously took into account the now overturned convictions at Siegelman's original sentencing. Considering those same allegations at the new sentencing hearing might persuade the judge to reimpose the same sentence, but it's hard to see how the overturned convictions would justify a longer sentence. The rationale for the Justice Department's request, if there is one, will be revealed at the new sentencing hearing -- maybe earlier if the AP discloses the contents of the government's letter in more detail.
Eric Holder, perhaps fearful that reigning in the prosecutors would lead to criticism that he's protecting a Democratic politician, seems to have washed his hands of the mess. Despite calls for Holder to examine Siegelman's prosecution (including, most recently, a request made by 75 former state attorneys general) and to dismiss the charges if they are tainted by prosecutorial misconduct -- the same benefit he gave to Ted Stevens -- Holder refuses to review Siegelman's case.
Things look bleak for Siegelman at this point. Most of his convictions were affirmed on appeal, his request for the full court to rehear the panel's unanimous appellate decision will probably be denied, and Holder won't intervene. Even if Karl Rove finally testifies as part of a House Judiciary Committee investigation, Congress has no power to free Siegelman from prison. President Obama could use the Scooter Libby precedent to commute Siegelman's sentence, but he isn't likely to undermine Holder's decision to let it be -- unless, perhaps, the Justice Department gets the 20 years it seeks. It seems inevitable that Siegelman will be returning to prison -- it's just a question of how long he'll be there.
As an aside, this post makes a convincing case that Siegelman is being punished for conduct in which other politicians -- including Texas Governors Rick Perry and George W. Bush -- have routinely engaged.