Billy and Marge Burke of Gilmer County, W.Va., have been married 54 happy years.

That’s four years less than Sen. Robert Byrd (D) has served the Mountain State on Capitol Hill.

And when Byrd was up for re-election for his ninth Senate term in 2006, the Burkes — who are in Denver this week as part of the West Virginia delegation — naturally put a “Robert Byrd for Senate” bumper sticker on their new Cadillac.

Billy Burke recalled that when he happened to mention to Byrd in a recent phone call that the bumper sticker was still firmly affixed to his rear fender, Byrd didn’t miss a beat when he replied, “Leave it there. You’ll need it” in 2012.

Such is the thinking of a man who, despite continued speculation, defies any predictions about when he might leave Congress.

And although some West Virginia insiders occasionally ponder the question of who could follow Byrd in the Senate (much in the same way businesses create succession plans), the resounding consensus is that no one could ever really come after Robert Byrd.

“He’s truly the man of the century for our state — the last century and the current century,” Rep. Nick Rahall said at West Virginia’s delegate breakfast on Wednesday morning.

“You can’t fill those shoes,” Gov. Joe Manchin (D) said. “We don’t talk about that. … If something changes, someone will step to the forefront.” But right now, any speculation about what comes after Byrd “is more of a media and national concern than it ever has been for the state.”

Media reports have detailed the 90-year-old Byrd’s health challenges this Congress, especially after a nearly three-week hospital stay in late February and early March, and another hospital scare over the summer. Roll Call reported that in April, Senate leaders privately discussed how to replace Byrd as head of the Appropriations Committee before backing away from the idea after Byrd made a round of calls promising to be more vigorous in his chairmanship duties.

Byrd made good on that promise and continues to find ways to prove his vigor.

Though he’s not in Denver this week, Byrd is taking turns in Washington gaveling the Senate into and out of session in what has become a standard practice to keep President Bush from making recess appointments. His office said this week that he remains in contact with West Virginia officials on the ground in Denver and has several top staffers at the convention. He’s also managed to steal some headlines in this month of presidential convention news by being featured in a story about his zest for his Senate job in September’s edition of GQ.

Still, some West Virginia political insiders will quietly speculate about what will follow in West Virginia when Byrd leaves the Senate.

If there is a vacancy in the Senate, it falls to the governor to make an appointment until a special election can be held.

Manchin is running for, and expected to win, re-election. So, any Senate vacancy before the 2012 cycle (when the seat is up) will likely fall to Manchin to fill.

Manchin is also the most often mentioned name to take over the Senate job when it becomes open. One West Virginia insider pointed out that there’s a lot of talk among top Democratic leaders about the possible scenarios given Manchin’s likely interest in Capitol Hill.

Unless a Senate opening occurs near the end of Manchin’s gubernatorial term, some analysts say it would be awkward for the governor to appoint himself. He could, however, appoint a placeholder, say a close confidant like West Virginia Democratic Party Chairman Nick Casey, to hold the seat until a special election could be held.

Casey said Wednesday that any talk about him getting a Senate appointment is merely a Charleston rumor and “not a possibility.”

But one West Virginia Democrat said it would be natural for anyone with interest in the Senate to shy away from the spotlight. Given Byrd’s universal popularity in West Virginia, anyone who is viewed to be laying the groundwork to replace Byrd would be scorned.

“People don’t want their names mentioned. They’d dive under the table if they knew their names were being put out there,” the West Virginia source said.

On the GOP side, Rep. Shelley Moore Capito, the lone Republican in the state’s Congressional delegation, is the most often mentioned name for a possible Senate run, and she is one candidate who could give Manchin a race. The two families — the Manchins and the Moores — have long been allies despite coming from different parties.

But Capito has more pressing issues to take care of before she could consider a Senate bid. This fall she’s facing a tough re-election battle from one of Byrd’s former top aides, Anne Barth. Byrd has already stumped for Barth since she decided to run just before the state filing deadline in January. Barth has also picked up strong support from the Democratic Congressional Campaign Committee and the pro-abortion-rights group EMILY’s List.

Another well-known Republican who has been mentioned as a possible Senate candidate is West Virginia Secretary of State Betty Ireland.

Marge Burke said Wednesday that there seems to be a lot of backroom gossip about who would replace Byrd in the Senate, “but I personally don’t try to think about that.”

Billy Burke added that “while physically [Byrd] has some problems, his mind is still extremely strong.” And even though Byrd is not in Denver this week, “his heart is here and his mind is here.”