Senate Majority Leader Harry Reid (D., Nev.) has already gone to great lengths to prevent a vote on President Obama’s jobs package in its original form. However, even now that Reid has amendment the bill to include a $5.6 percent “millionaire’s surtax” to cover its $450 billion price tag, it’s looking like Democrats won’t even be able to muster a simply majority in support.

The Senate will vote this evening on the amended package. With all 47 Republicans planning to oppose the measure, Senate Democrats are scrambling to avoid an embarrassing outcome. Majority Whip Dick Durbin (D., Ill.) said Monday that he could lose up to four Democrats, which would amount to a 49 to 51 defeat for the legislation that Obama has repeatedly chastised Republicans for refusing to pass. 

Sens. Ben Nelson (D., Neb.), Joe Manchin (D., W. Va.), and Jon Tester (D., Mont.), all of whom represent conservative states and are facing difficult reelections in 2012, are likely to vote no. Furthermore, Sen. Jeanne Shaheen (D., N.H.), a supporter of the bill, has announced a scheduling conflict and may miss the vote. She is scheduled to be in Boston today to receive the “New Englander of the Year” award from a regional business council.

Shaheen’s spokesman said the senator is prepared to return to Washington “if her vote is needed for passage.” But given the 60-vote threshold to end a Republican filibuster, passage is out of the question. It is simply a matter of Democrats and the president hoping to suffer the least amount of political embarrassment before they can immediately begin to blame Republicans for being obstructionists.

UPDATE: The White House is in full spin mode:

“The test is not unanimous support among Democrats,” a senior White House official told reporters Tuesday morning, noting that rarely does the entire Democratic caucus vote in lockstep on any bill.

The focus, the official said, should be on Republicans’ unanimous opposition to the jobs bill — even though they have failed to present an alternative that would create jobs immediately.

“They’re a party in unanimity — voting against things that in normal times” would be considered popular and bipartisan such as extending the payroll tax relief and rebuilding aging roads and bridges, the official said.

“There’s a bigger picture here…,” the official continued. “You’re obsessing about whether we’re going to get 50 or 51.”

More here.

UPDATE II: Sen. Joe Lieberman (I., Ct.) just announced on the Senate floor that while he plans to vote for cloture on the president’s jobs bill, but would vote against final passage.

UPDATE III: Sen. Jim Webb (D., Va.), citing objections over the millionaires’ surtax as well as the timing of the bill, said he would be voting no on cloture. Assuming Sen. Shaheen does not cancel her award ceremony, that means we’re now looking at a ceiling of 48 votes for the president’s jobs bill.

UPDATE IV: Webb’s office clarifies, says the senator will vote yes on cloture, but “cannot support final passage of the bill in its current form.”

UPDATE V: The Senate will hold the vote open for Sen. Shaheen, who will return to Washington to support the bill.