Former Virginia governor Robert F. McDonnell speaks to reporters after his sentencing in January. (Alex Wong/Getty Images)

A federal appeals court Thursday rejected former Virginia governor Robert F. McDonnell’s request to stay out of prison while he pursues a challenge with the Supreme Court, prompting him to turn immediately to the nation’s top judicial authority in a final bid for continued freedom.

Unless the Supreme Court intervenes, experts said, the popular politician once considered for the 2012 Republican vice presidential nomination could be behind bars within a few months, perhaps even sooner. In a filing directed to Chief Justice John G. Roberts Jr., McDonnell’s attorneys argued that it was technically possible for the former governor to be jailed as soon as Aug. 27, when his case receives its final, formal stamp.

The Supreme Court offers his last hope to avoid that.

Without saying exactly why, the U.S. Court of Appeals for the 4th Circuit declined Thursday to declare that a previous ruling granting McDonnell bond would remain in effect while he prepared his petition to the nation’s highest court. The appeals court also refused to delay putting its formal, final stamp on the case.

McDonnell said in a statement that he was “saddened” by the ruling, and his attorneys asked the Supreme Court to allow him to remain out on bail while they worked to persuade the justices to hear his case. The attorneys argued that the Supreme Court was likely to want to take up the matter because McDonnell’s convictions threatened to criminalize routine dealings between politicians and people who give them something.

“The theory on which Gov. McDonnell was convicted is stunningly broad, historically unprecedented, and directly in conflict with decisions of this Court and three Circuits,” McDonnell’s attorneys wrote. “There is at least a reasonable probability that this Court will want to weigh in on such an important revolution in federal corruption law — one that would ‘wreak havoc’ on ‘the democratic process.’ ”

If the Supreme Court does not intervene, McDonnell’s case would get its final, formal stamp in one week, then be sent back to a lower court judge to pick a date by which McDonnell has to report to prison, experts said. Federal prison officials would be tasked with selecting a facility appropriate for the former governor, and he would probably be imprisoned within a few months, experts said.

In his statement, McDonnell continued to assert his innocence and vowed to press on.

“I ask my exceptional friends across the nation to continue to support and pray for me and my family during this agonizing time,” McDonnell said. “I thank God for His abundant grace and strength as I continue this difficult journey.”

U.S. Attorney Dana Boente, whose prosecutors in the Eastern District of Virginia handled the case, declined to comment for this article.

McDonnell and his wife, Maureen, were convicted in September of public corruption for lending the prestige of the governor’s office to Richmond businessman Jonnie R. Williams Sr. in exchange for $177,000 in loans, vacations and luxury goods. Jurors concluded unanimously that the couple lent Williams their “official” help — arranging meetings for him with state officials, allowing him to use the governor’s mansion and advocating inside government for his product — for what were effectively bribes.

The former governor was sentenced to two years in prison; his wife to a year and a day. Both appealed their convictions largely on the argument that they neither performed nor promised to perform any “official acts” for Williams and that jurors were wrongly instructed on the topic. An appeals court panel rejected that assertion in the former governor’s case; his wife’s challenge is proceeding separately, with oral arguments scheduled for Oct. 29.

McDonnell has until Nov. 9 to file a petition asking the Supreme Court to actually take up his case, though his challenge now is persuading the justices to either give him bail — or to delay the formal, final stamp of the appeals court ruling — until then.

To win such a reprieve, McDonnell must convince Roberts — or the full court, if Roberts decides that is necessary — that there is a “reasonable probability” that four justices would agree to review his case, that there is a “fair prospect” a majority would ultimately rule in his favor and that he would suffer irreparable harm if his request were denied.

In a filing Thursday, McDonnell’s attorneys argued that he “may well complete his 2-year prison sentence” if sent to prison while they worked on his Supreme Court petition, and that would be unfair if he were to later “have the critical legal premise for the conviction invalidated, or the fundamental unfairness of the trial confirmed.”

The attorneys argued that the Supreme Court was likely to want to weigh in on what an “official act” must be in a federal bribery case and clarify the important “legal line in separating lawful politics from criminal corruption.” They asserted that McDonnell’s case was “the first time in the history of the Nation that an official has been convicted of corruption despite never putting an official thumb on the scales of any actual government decision.”

McDonnell’s attorneys also argued that jurors were not questioned thoroughly enough about pretrial publicity. The arguments are ones that McDonnell has raised many times before and that prosecutors have vigorously disputed.

Some experts have said that McDonnell’s chances of winning Supreme Court review are slim. The Supreme Court receives about 10,000 petitions each year and hears oral arguments in only about 75 or 80 cases, according to information on the court’s Web site. The court typically takes about six weeks to act on the petitions it receives, though it will likely move quickly on McDonnell’s request to stay out of prison.