Sen. Robert Byrd’s (D-W.Va.) future as the Appropriations chairman likely hinges on his follow-through today on a hearing he scheduled on the Iraq War supplemental spending bill.

If Byrd, 90, has any difficulty chairing the hearing, his Democratic colleagues could have further reason to try to displace him atop the powerful panel. Or, if Byrd were to postpone the hearing at the last minute or tap another Member to chair it, new questions are certain to arise over whether the ailing Senator is up for the job.

With the expectations seemingly set so high, Democrats on Tuesday said they are waiting to see the next move from Byrd, the longest-serving Senator and one of the chamber’s most revered. Byrd’s health has been diminishing recently, and last week a group of senior Democrats discussed whether their colleague was still fit for the grueling appropriations task.

Byrd has been confined to a wheelchair since February after suffering a fall at his home.

“If he doesn’t handle the hearing very well, or at all, more and more people are going to be hoping he and his staff make the right decision,” said one high-level Democrat, speaking on the condition of anonymity. “I believe the bar has been set very high. He’s third in line to the line of succession [for the presidency], and we’re looking at a $100 billion-plus appropriations bill.”

“If he nails it, he has it,” said another Senate Democratic source of Byrd’s hold on the chairmanship. “If he doesn’t, it’s anybody’s guess. That’s the risk if he does it.”

Byrd’s office alerted appropriators of the Wednesday hearing on Monday afternoon but didn’t formally announce it until after 4 p.m. Tuesday. Office of Management and Budget Director Jim Nussle is expected to testify at the two-hour noon session.

“The whole way it was noticed and handled is extremely unusual,” noted one Senate Democratic aide. “It would raise questions.”

Logistics aside, Senators in both parties quietly acknowledged Tuesday that Byrd will be watched carefully to determine if he can manage the critical proceedings with vigor and competence.

“If he doesn’t [chair the hearing], it will be because he himself has declined to do it,” said Sen. Frank Lautenberg (D-N.J.), a fellow appropriator. “Questions have been raised [about Byrd’s capabilities] primarily as rumor and speculation. … We’re not going to have a coup here.”

Democratic leaders have been unwilling to try to remove Byrd from the Appropriations chairmanship, hoping to subtly persuade him to voluntarily cede the gavel. But the Democrats’ posture could change after Wednesday’s hearing.

It’s unclear whether Byrd — armed by a powerful staff — would continue to dig in. Byrd has told colleagues that he can and will do the Appropriations job for the foreseeable future.

Byrd might be looking to today’s hearing to shore up his support among colleagues, just as they will be looking to see if he measures up. Byrd has had a spotty record chairing the committee over the past year, even turning to other Democrats to shepherd key spending bills through the chamber on his behalf.

Doing little to tamp down the Democrats’ expectations, Senate Majority Whip Dick Durbin (D-Ill.) said Tuesday: “We have an important bill, over $100 billion in spending. We have critical questions to be asked about the wars in Iraq and Afghanistan, and a lot of Member interest in other things to be added to the supplemental. It’s a very important hearing, and Sen. Byrd announced that it’ll be held on Wednesday, and I’ll be there.”

“I can tell you that Sen. Byrd is engaged and he is going to chair the hearing tomorrow and I have no reason to believe that he’ll do anything different than he has in the last year,” said fellow appropriator and Senate Democratic Conference Secretary Patty Murray (Wash.).

Senate Democratic sources insisted that despite Senators’ conversations about his fitness, Democratic leaders did not force Byrd to hold Wednesday’s supplemental hearing. Rather, those Democrats said Byrd’s staff scheduled it to reinforce he still has the stamina to lead the panel.

Additionally, Byrd’s staff has let Democratic leaders know that the chairman plans on managing the supplemental spending debate on the floor — an often arduous and time-consuming task that he has delegated to more junior members on the panel in recent years. Murray took on the job last year.

“It’s his responsibility,” Durbin said when asked about Byrd’s floor management duties. “He can either do it or as some members do, he can delegate to others. It’s entirely up to him.”

Durbin added, “We’ll all be there to help, all of the subcommittee chairs and other members of the committee. We want this done, and we want it done professionally, and we’re going to help the Senator in any way that he wants.”